They are self propelled but when cutting they are towed by the tractor with the drive clutched in, so I doesnt matter about the speed. The self propultion is great cos if you get stuck up a too steep of a hill you put them in drive and it drives you out, also you can unhitch and drive them individually into the shed or whatever.
The thing that makes them so great is that you dont rely on traction to the ground to turn the blades, the engine does that for you. I tow them with a 12 Hp tractor.
the mowers cost total £7, all worked with little effort, on has a new engine, but that was for fun and not necessary.
I actually never use them, so if you wanna collect theyre for sale /forums/images/graemlins/laugh.gif