Yes, projectors under £860 can absolutely be worth buying if you want a large-screen image without paying premium home-cinema money. In that range you can still find good 1080p models, some basic 4K-capable options, and useful living-room or portable designs that handle films, sports, and casual gaming well.
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The usual compromises are black levels, HDR performance, lens controls, fan noise, and overall refinement. Under £860 is also where advertised brightness and smart features can look better on paper than they do in real rooms, so choosing a well-reviewed model matters more than chasing the longest feature list.
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If you care a lot about dark-room movie quality, stronger gaming performance, or easier placement, stretching the budget can still be worthwhile. But for many buyers, a sub-£860 projector is a sensible value choice as long as you expect solid all-round performance rather than top-tier cinema results.