I got the Aldi/Lidl one, I think a shade under £30. It's the first one I have had, and I wonder how I managed without it. I've just completed a refurb of my old Raleigh MTB in half the time I expected, with no sore knees or back. It's a bit flimsy (and yes, the legs are easy to trip over) but OK for home use. I clamp it on the top tube. It's a fairly heavy steel frame, so I haven't worried too much about damaging the tube, but in fact I did most of the work with the bike clamped at its centre of balance, so there was no need to clamp it tight - just enough to keep it still.