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By way of an update - I got the Dyson V8 and it is fantastic!
Brilliant suction, picks up right into the edges and corners, lightweight, lots of great attachments, boost button (which I rarely need because the suction is so good), no problem with dog hair, etc etc.
Yes it has a small dustbin but it is so easy to empty that it is no bother at all.
Yes, the battery only lasts for approx 20 minutes but the machine is so good, I can have most of my vacuuming done in 20 mins.
I kept my old upright, corded vacuum as my 'main' one - but haven't used it once!