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SPECS
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Shark BU3521UKTSB Review | 52 Data compared

Avg. price:~£210Suction power (AW):140 AWBattery runtime:40 minutesCapacity:0.42 LWeight:2.7 kg

Shark BU3521UKTSB Review: Compare 52 technical specifications and user reviews to see how this product ranks in the Vacuum Cleaners category and whether it is worth buying.

7.6

Overall score

Score
7.6/ 10
✕
What it is
An overall evaluation of the vacuum cleaner's quality, based on technical analysis and user reviews.
When it matters
When you need a quick reference for identifying the best vacuum cleaners on the market.
Score distribution
â–¼
<55-66-77-88-99-10
â–² Better than 79% of models
Score components

80%

7.3

Technical Score

20%

8.7

User score

â–²Better than 79% of vacuum-cleaners
7.3

Technical Score

Technical score
7.3/ 10
✕
What it is
An assessment of the vacuum cleaner's technical performance across six key areas: performance, battery and power supply, filtration, attachments, design, and smart features.
When it matters
When you want to compare vacuum cleaners by cleaning performance, specifications, and available features.
Score distribution
â–¼
<55-66-77-88-99-10
â–² Better than 74% of models
Score components

28%

6.8

Performance

22%

6.2

Battery

18%

8.0

Filtration

14%

9.2

Attachments

10%

7.0

Design

8%

7.9

Smart features

â–²Better than 74% of vacuum-cleaners
8.7

User score

User score
8.7/ 10
✕
What it is
A rating that combines user reviews with the total number of reviews received by the vacuum cleaner.
When it matters
When you want to know how a vacuum cleaner performs in everyday use and how reliable owners find it over time.
Score distribution
â–¼
<55-66-77-88-99-10
â–² Better than 86% of models
Score components

70%

9.0

User ratings

30%

7.9

Number of reviews

Based on 635 buyer reviews from online shops.
Read buyer reviews on Amazon →
How we calculate this
User ratings – average star rating across all shop listings, weighted by how many reviews each has, on a 1–10 scale.
Number of reviews – how many buyer reviews the product has, on a logarithmic scale; the 8% most-reviewed models in the category get 10.
â–²Better than 86% of vacuum-cleaners
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Best prices

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Best rankings

Available: ranking among products currently available (including other versions of this product).All: ranking among all products in the database.
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Verdict

The Shark BU3521UKTSB is a 2-in-1 cordless stick and detachable handheld vacuum cleaner weighing 2.7 kg, operating on a 21.6V lithium-ion battery that delivers up to 40 minutes of runtime in Eco mode. Key characteristics include an automated 1.3-litre bagless Clean & Charge base that holds up to 30 days of debris, Floor Detect technology that auto-adjusts suction power across surfaces, and an Anti Hair Wrap self-cleaning brush roll with integrated LED headlights. Major pros highlight its hygienic, multi-stage HEPA filtration with an Anti-Allergen Complete Seal trapping 99.9% of dust, exceptionally lightweight maneuverability, and a dedicated bundle containing a motorized pet tool and a crevice tool. Conversely, notable cons include a small 0.42-litre on-vacuum dust cup capacity, a relatively long 4.5 to 5-hour battery charge time, and a significant drop in battery life when utilizing its maximum suction Boost mode.

Technical Specifications of vacuum cleaner Shark BU3521UKTSB

Technical Score
Technical score
7.3/ 10
✕
What it is
An assessment of the vacuum cleaner's technical performance across six key areas: performance, battery and power supply, filtration, attachments, design, and smart features.
When it matters
When you want to compare vacuum cleaners by cleaning performance, specifications, and available features.
Score distribution
â–¼
<55-66-77-88-99-10
â–² Better than 74% of models
Score components:

28%

6.8

Performance

22%

6.2

Battery

18%

8.0

Filtration

14%

9.2

Attachments

10%

7.0

Design

8%

7.9

Smart features

7.3
Shark BU3521UKTSB has a technical score of 7.3 points, which is higher than 74.1% of vacuum cleaners.
User score
User score
8.7/ 10
✕
What it is
A rating that combines user reviews with the total number of reviews received by the vacuum cleaner.
When it matters
When you want to know how a vacuum cleaner performs in everyday use and how reliable owners find it over time.
Score distribution
â–¼
<55-66-77-88-99-10
â–² Better than 86% of models
Score components

70%

9.0

User ratings

30%

7.9

Number of reviews

Based on 635 buyer reviews from online shops.
Read buyer reviews on Amazon →
How we calculate this
User ratings – average star rating across all shop listings, weighted by how many reviews each has, on a 1–10 scale.
Number of reviews – how many buyer reviews the product has, on a logarithmic scale; the 8% most-reviewed models in the category get 10.
8.7
Shark BU3521UKTSB has a user score of 8.68 points, which is higher than 86% of vacuum cleaners.
Popularity
Popularity
7.9/ 10
✕
What it is
An indicator based on the number of reviews received by the vacuum cleaner.
When it matters
When you prefer a vacuum cleaner that has been chosen and reviewed by many other buyers.
Score distribution
â–¼
<55-66-77-88-99-10
â–² Better than 71% of models
Popularity:
Shark BU3521UKTSB has a popularity score of 7.9 points, which is higher than 71% of vacuum cleaners.
7.9
Shark BU3521UKTSB has a popularity score of 7.9 points, which is higher than 71% of vacuum cleaners.
Ratio quality/price
Value for money
8.2/ 10
✕
What it is
An indicator that combines the vacuum cleaner's overall score with its price.
When it matters
When you are looking for a vacuum cleaner with a good balance between quality and price.
Score distribution
â–¼
<55-66-77-88-99-10
â–² Better than 83% of models
Score components:

60%

7.6

Overall score

40%

9.4

Price

8.2
Shark BU3521UKTSB has a value-for-money score of 8.2 points, which is higher than 82.8% of vacuum cleaners.
Suction power (AW)
140 AW
Suction power (AW)
140 AW
â–¼ Worse than 59% of models
Market range: <40 AW – >280 AW
This vacuum cleaner has a suction power of 140 AW, which is lower than that of 59.4% of vacuum cleaners and equal to that of 1.2% of vacuum cleaners.
Suction power (kPa)
?
Airflow
?
Motor type
brushless
Power consumption
240 W
Power consumption
240 W
â–² Better than 81% of models
Market range: <165 W – >899 W
This vacuum cleaner draws 240 W, which is lower than the power consumption of 81.4% of vacuum cleaners and equal to that of 1.5% of vacuum cleaners.
Show more
Cordless
yes
Cordless
yes
â–² Better than 51% of models
This vacuum cleaner works cordlessly. 49.5% of vacuum cleaners offer cordless operation.
Battery runtime
40 minutes
Battery runtime
40 minutes
â–¼ Worse than 64% of models
Market range: <30 minutes – >70 minutes
This vacuum cleaner offers a battery runtime of 40 minutes, which is shorter than that of 64.1% of vacuum cleaners and equal to that of 18.6% of vacuum cleaners.
Charging time
5 hours
Charging time
5 hours
â–¼ Worse than 74% of models
Market range: <3 hours – >5 hours
This vacuum cleaner charges in 5 hours, which is slower than 73.8% of vacuum cleaners and equal to 20.4% of vacuum cleaners.
Battery capacity
2,500 mAh
Battery capacity
2,500 mAh
â–² Better than 48% of models
Market range: <2k mAh – >3.6k mAh
This vacuum cleaner has a battery capacity of 2,500 mAh, which is larger than that of 48.1% of vacuum cleaners and equal to that of 24.7% of vacuum cleaners.
Battery voltage
21.6 V
Battery voltage
21.6 V
â–¼ Worse than 60% of models
Market range: <18 V – >28.8 V
This vacuum cleaner uses a battery voltage of 21.6 V, which is lower than that of 59.8% of vacuum cleaners and equal to that of 16.5% of vacuum cleaners.
Show more
Filter class
hepa
Filter class
hepa
â–¼ Worse than 38% of models
This vacuum cleaner uses filter class hepa, which is more advanced than the class used by 16% of vacuum cleaners and the same as the class used by 46% of vacuum cleaners.
Minimum overall efficiency
99.97%
Minimum overall efficiency
99.97%
â–² Better than 59% of models
Market range: <95 % – >99.99 %
This vacuum cleaner reaches 99.97% minimum overall efficiency, which is higher than that of 59.1% of vacuum cleaners and equal to that of 19.4% of vacuum cleaners.
Suitable for allergy sufferers
yes
Suitable for allergy sufferers
yes
â–² Better than 18% of models
This vacuum cleaner is suitable for allergy sufferers. 82.4% of vacuum cleaners are allergy-friendly.
Capacity
0.42 L
Capacity
0.42 L
â–¼ Worse than 90% of models
Market range: <0.44 L – >4 L
This vacuum cleaner has a dust capacity of 0.42 L, which is smaller than that of 90.2% of vacuum cleaners and equal to that of 0.3% of vacuum cleaners.
Bagless
yes
Bagless
yes
â–² Better than 21% of models
This vacuum cleaner uses a bagless design. 78.6% of vacuum cleaners use this setup.
Show more
Main brush type
roll brush
Roller type
multi-surface
Anti-tangle brush
yes
Anti-tangle brush
yes
â–² Better than 74% of models
This vacuum cleaner includes an anti-tangle brush. 25.7% of vacuum cleaners include this feature.
Mini motorized brush
yes
Mini motorized brush
yes
â–² Better than 73% of models
This vacuum cleaner includes a mini motorized brush. 26.9% of vacuum cleaners include this attachment.
Suitable for pet owners
yes
Suitable for pet owners
yes
â–² Better than 28% of models
This vacuum cleaner is suitable for pet owners. 72% of vacuum cleaners handle pet hair well.
Show more
Vacuum type
stick
Weight
2.7 kg
Weight
2.7 kg
â–² Better than 70% of models
Market range: <2.15 kg – >7.1 kg
This vacuum cleaner weighs 2.7 kg, which is lower than the weight of 70.1% of vacuum cleaners and equal to that of 2.4% of vacuum cleaners.
2-in-1 design
yes
2-in-1 design
yes
â–² Better than 47% of models
This vacuum cleaner offers a 2-in-1 design. 53% of vacuum cleaners offer this flexible format.
Self-standing
no
Self-standing
no
â–¼ Worse than 19% of models
This vacuum cleaner does not stand on its own. 18.9% of vacuum cleaners offer this convenience.
Adjustable tube height
no
Adjustable tube height
no
â–¼ Worse than 47% of models
This vacuum cleaner does not include adjustable tube height. 47.4% of vacuum cleaners offer this ergonomic feature.
Show more
Auto suction adjustment
yes
Auto suction adjustment
yes
â–² Better than 80% of models
This vacuum cleaner supports automatic suction adjustment. 19.9% of vacuum cleaners support this feature.
Dust particle sensor
no
Dust particle sensor
no
â–¼ Worse than 8% of models
This vacuum cleaner does not include a dust particle sensor. 8% of vacuum cleaners include this feature.
LED display
yes
LED display
yes
â–² Better than 74% of models
This vacuum cleaner includes an LED display. 25.9% of vacuum cleaners include this interface feature.
Nozzle light
yes
Nozzle light
yes
â–² Better than 57% of models
This vacuum cleaner includes a nozzle light. 43.4% of vacuum cleaners include this visibility feature.
Mopping support
no
Mopping support
no
â–¼ Worse than 4% of models
This vacuum cleaner does not support mopping. 3.7% of vacuum cleaners support this multi-function feature.

Shark BU3521UKTSB vs the average vacuum cleaner

246810TotalPerformanceBatteryFiltrationAttachmentsDesignSmart features
  • Cordless operation
    Cordless
    yes
    â–² Better than 51% of models
    This vacuum cleaner works cordlessly, the average vacuum cleaner does not.
  • Includes mini motorized brush
    Mini motorized brush
    yes
    â–² Better than 73% of models
    This vacuum cleaner includes a mini motorized brush, the average vacuum cleaner does not.
  • Includes anti-tangle brush
    Anti-tangle brush
    yes
    â–² Better than 74% of models
    This vacuum cleaner includes an anti-tangle brush, the average vacuum cleaner does not.
  • Automatic suction adjustment
    Auto suction adjustment
    yes
    â–² Better than 80% of models
    This vacuum cleaner supports automatic suction adjustment, the average vacuum cleaner does not.
  • Includes removable battery
    Removable battery
    yes
    â–² Better than 61% of models
    This vacuum cleaner includes a removable battery, the average vacuum cleaner does not.
  • Includes full bin indicator
    Full bin indicator
    yes
    â–² Better than 73% of models
    This vacuum cleaner includes a full bin indicator, the average vacuum cleaner does not.
  • Includes nozzle light
    Nozzle light
    yes
    â–² Better than 57% of models
    This vacuum cleaner includes a nozzle light, the average vacuum cleaner does not.
  • Includes LED display
    LED display
    yes
    â–² Better than 74% of models
    This vacuum cleaner includes an LED display, the average vacuum cleaner does not.
  • 8.5% higher user score
    User score
    8.7/ 10
    ✕
    What it is
    A rating that combines user reviews with the total number of reviews received by the vacuum cleaner.
    When it matters
    When you want to know how a vacuum cleaner performs in everyday use and how reliable owners find it over time.
    Score distribution
    â–¼
    â–¼
    <55-66-77-88-99-10
    Shark BU3521UKTSB
    the average vacuum cleaner
    ★ Better than 94% of models
    Shark BU3521UKTSB has a higher user score than the average vacuum cleaner (8.68 vs 8.000).
    8.68 vs 8
  • 6.6% better value for money
    Shark BU3521UKTSB offers better value for money than the average vacuum cleaner (8.15 vs 7.6).
    8.15 vs 7.65
  • 360 W lower power consumption
    Power consumption
    240 W
    â–² Better than 81% of models
    Market range: <165 W – >899 W
    This vacuum cleaner draws less power than the average vacuum cleaner (240 W vs 600 W).
    240 W vs 600 W
  • 1 more power levels
    Number of speeds
    3
    â–² Better than 56% of models
    Market range: <1 – >4
    This vacuum cleaner offers more speed levels than the average vacuum cleaner (3 vs 2).
    3 vs 2
  • Cordless operation
    Cordless
    yes
    â–² Better than 51% of models
    This vacuum cleaner works cordlessly, the average vacuum cleaner does not.
  • Includes removable battery
    Removable battery
    yes
    â–² Better than 61% of models
    This vacuum cleaner includes a removable battery, the average vacuum cleaner does not.
  • Includes battery indicator
    Battery level indicator
    yes
    â–² Better than 53% of models
    This vacuum cleaner includes a battery level indicator, the average vacuum cleaner does not.
  • Includes full bin indicator
    Full bin indicator
    yes
    â–² Better than 73% of models
    This vacuum cleaner includes a full bin indicator, the average vacuum cleaner does not.
  • 0.02 % higher filtration efficiency
    Minimum overall efficiency
    99.97 %
    â–² Better than 59% of models
    Market range: <95 % – >99.99 %
    This vacuum cleaner has higher filtration efficiency than the average vacuum cleaner (100 % vs 99.95 %).
    99.97 % vs 99.95 %
  • Includes mini motorized brush
    Mini motorized brush
    yes
    â–² Better than 73% of models
    This vacuum cleaner includes a mini motorized brush, the average vacuum cleaner does not.
  • Includes anti-tangle brush
    Anti-tangle brush
    yes
    â–² Better than 74% of models
    This vacuum cleaner includes an anti-tangle brush, the average vacuum cleaner does not.
  • 25.4% lower weight
    Weight
    2.7 kg
    â–² Better than 70% of models
    Market range: <2.15 kg – >7.1 kg
    This vacuum cleaner is lighter than the average vacuum cleaner (2.7 kg vs 3.62 kg).
    2.7 kg vs 3.62 kg
  • Newer release date
    Release date
    2024
    â–² Better than 82% of models
    Market range: <2k – >2k
    This vacuum cleaner has a newer release date than the average vacuum cleaner (2024 vs 2021).
    Released in June 2024.
    2024 vs 2021
  • Automatic suction adjustment
    Auto suction adjustment
    yes
    â–² Better than 80% of models
    This vacuum cleaner supports automatic suction adjustment, the average vacuum cleaner does not.
  • Includes nozzle light
    Nozzle light
    yes
    â–² Better than 57% of models
    This vacuum cleaner includes a nozzle light, the average vacuum cleaner does not.
  • Includes LED display
    LED display
    yes
    â–² Better than 74% of models
    This vacuum cleaner includes an LED display, the average vacuum cleaner does not.
  • More operating noise
    Noise level (Min-Max)
    80-84.4 dB
    â–¼ Worse than 89% of models
    Market range: <65 dB – >83 dB
    This vacuum cleaner is noisier than the average vacuum cleaner (80-84.4 dB vs 77-77 dB).
    80-84.4 dB vs 77-77 dB
  • 0.58 L smaller dust container
    Capacity
    0.42 L
    â–¼ Worse than 90% of models
    Market range: <0.44 L – >4 L
    This vacuum cleaner has a smaller dust capacity than the average vacuum cleaner (0.4 L vs 1 L).
    0.42 L vs 1 L
  • 1 hours slower charging
    Charging time
    5 hours
    â–¼ Worse than 74% of models
    Market range: <3 hours – >5 hours
    This vacuum cleaner charges slower than the average vacuum cleaner (5 hours vs 4 hours).
    5 hours vs 4 hours
  • 10 minutes shorter runtime
    Battery runtime
    40 minutes
    â–¼ Worse than 64% of models
    Market range: <30 minutes – >70 minutes
    This vacuum cleaner offers shorter battery runtime than the average vacuum cleaner (40 minutes vs 50 minutes).
    40 minutes vs 50 minutes
  • No cyclonic technology
    Cyclonic technology
    no
    â–¼ Worse than 71% of models
    This vacuum cleaner does not use cyclonic technology, the average vacuum cleaner does.
  • 51 mm narrower cleaning path
    Cleaning path width
    209 mm
    â–¼ Worse than 98% of models
    Market range: <230 mm – >309 mm
    This vacuum cleaner has a narrower cleaning path than the average vacuum cleaner (209 mm vs 260 mm).
    209 mm vs 260 mm
  • 10 AW lower suction power
    Suction power (AW)
    140 AW
    â–¼ Worse than 59% of models
    Market range: <40 AW – >280 AW
    This vacuum cleaner has lower suction power than the average vacuum cleaner (140 AW vs 150 AW).
    140 AW vs 150 AW
  • 0.6 V lower voltage
    Battery voltage
    21.6 V
    â–¼ Worse than 60% of models
    Market range: <18 V – >28.8 V
    This vacuum cleaner has a lower battery voltage than the average vacuum cleaner (21.6 V vs 22.2 V).
    21.6 V vs 22.2 V
  • 40% more expensive
    Shark BU3521UKTSB is more expensive than the average vacuum cleaner (£210 vs £150).
    £210 vs £150
  • More operating noise
    Noise level (Min-Max)
    80-84.4 dB
    â–¼ Worse than 89% of models
    Market range: <65 dB – >83 dB
    This vacuum cleaner is noisier than the average vacuum cleaner (80-84.4 dB vs 77-77 dB).
    80-84.4 dB vs 77-77 dB
  • No cyclonic technology
    Cyclonic technology
    no
    â–¼ Worse than 71% of models
    This vacuum cleaner does not use cyclonic technology, the average vacuum cleaner does.
  • 51 mm narrower cleaning path
    Cleaning path width
    209 mm
    â–¼ Worse than 98% of models
    Market range: <230 mm – >309 mm
    This vacuum cleaner has a narrower cleaning path than the average vacuum cleaner (209 mm vs 260 mm).
    209 mm vs 260 mm
  • 10 AW lower suction power
    Suction power (AW)
    140 AW
    â–¼ Worse than 59% of models
    Market range: <40 AW – >280 AW
    This vacuum cleaner has lower suction power than the average vacuum cleaner (140 AW vs 150 AW).
    140 AW vs 150 AW
  • 1 hours slower charging
    Charging time
    5 hours
    â–¼ Worse than 74% of models
    Market range: <3 hours – >5 hours
    This vacuum cleaner charges slower than the average vacuum cleaner (5 hours vs 4 hours).
    5 hours vs 4 hours
  • 10 minutes shorter runtime
    Battery runtime
    40 minutes
    â–¼ Worse than 64% of models
    Market range: <30 minutes – >70 minutes
    This vacuum cleaner offers shorter battery runtime than the average vacuum cleaner (40 minutes vs 50 minutes).
    40 minutes vs 50 minutes
  • 0.6 V lower voltage
    Battery voltage
    21.6 V
    â–¼ Worse than 60% of models
    Market range: <18 V – >28.8 V
    This vacuum cleaner has a lower battery voltage than the average vacuum cleaner (21.6 V vs 22.2 V).
    21.6 V vs 22.2 V
  • 0.58 L smaller dust container
    Capacity
    0.42 L
    â–¼ Worse than 90% of models
    Market range: <0.44 L – >4 L
    This vacuum cleaner has a smaller dust capacity than the average vacuum cleaner (0.4 L vs 1 L).
    0.42 L vs 1 L
  • 89 mm deeper body
    Depth
    354 mm
    â–¼ Worse than 73% of models
    Market range: <170 mm – >440 mm
    This vacuum cleaner is deeper than the average vacuum cleaner (354 mm vs 265 mm).
    354 mm vs 265 mm

Graphic comparison of Shark BU3521UKTSB and other vacuum cleaners

No results found

Third-party reviews

Based on 635 buyer reviews from online shops.
Reviews last updated: July 2026 · How we calculate this
Read buyer reviews on Amazon →

What customers like about Shark BU3521UKTSB?

  • Convenient auto-empty docking system that holds up to 30 days of dirt
  • Lightweight and highly manoeuvrable, making it easy to clean stairs and under furniture
  • Strong suction power that effectively picks up pet hair and works well on both carpets and hard floors
  • Automatically detects and adjusts suction power based on the floor type
  • Anti Hair Wrap technology successfully prevents hair from tangling around the brush roll
  • Operates quietly during standard floor cleaning

What customers dislike about Shark BU3521UKTSB?

  • Battery life can feel limited, with some users stating it drains quickly on carpet and may not finish a large house
  • Plastic build quality can feel slightly cheap or less sturdy compared to premium competitors
  • The auto-empty process at the dock can be quite loud when active
  • Internal debris filters can occasionally clog before the main compartment is completely full
  • The unit does not stand upright on its own without being docked

Expert reviews

In-depth analysis and verdict from leading tech publications

I
independent.co.uk
07/01/2026
Summary of the review
6 best Shark vacuum cleaners, tried and tested by an expert
Q
quechoisir.org
27/06/2025
Summary of the review
Shark BU3521EU FloorDetect Cordless Vacuum Cleaner Review
(Translated)Show original

Video reviews

Hands-on testing, unboxing, and real-world video evaluations

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