Polo Bikes

I'd not get too stressed by sprockets on the front wheel from a safety pont of view. If you've got body parts heading toward a spinning wheel they're pretty likely to get mangled either way.

I think the front wheel is generally where the action is.. spokes or wheel covers can rub off someone's leg with not much problems, but if you got the teeth of a fixed sprocket rolling around and making contact, the potential for slashings is increased.

And yes its a gimmick, which doesnt make much sense IMHO. You mess up your back wheel, you put your spare back wheel from your front forks in its place - you still need a(nother) front wheel to cycle the bike.