we had a demo and only got as far as the gateway and got stuck! our fields take so long to fully dry out we would only end up using it for a few months so sent it back.
Predator Club Pro, wonderful machine, it picks up everything and apparently could even pick up water, but we haven't tried it. You need something to tow whatever you look at.
Personally I don't like the brush ones that are more of a sweeper and prefer the vac ones, we've had ours a couple of years and there are some bad points too, ours really needs one to drive and another to use the vacuum part, it can be quite heavy going and the muck can stick if too wet.
Most of the manufacturers will do a demo for you, we bought ours second hand though and I wouldn't be without it.