The interface looks pretty slick, but it's basically just offering a combination of:
"per point" bets - bog standard spread betting
"basic" bets - BetOnMarket-style bets, except a smaller range of options
"back players" bets - this looks interesting, but has two major issues:
1) People who are backed while trading well with play money get a share of the profits - I assume this is the profit of the back bets (as opposed to the play money profit), in which case if the traders are so successful, why are they still on play money?
2) For traders who are successful with real money, what incentive is there for making their porfolio public so that other people can back them? Do they get a share of the profits of the back bets placed on themselves? If not, then surely there is no incentive at all for going "public"?
Interesting idea though, surprised I only just heard of them from this thread...