I'm weighing in a bit late. But, I kinda like it. It looks cool and if anyone is dumb enough to run into it then I suppose they will have to face the consequences.
So, what about, say, a biker who is on the roundabout who gets knocked off his bike because the driver of the car entering the roundabout didn't see him? You'd be amazed at how often drivers don't see CARS already on a roundabout when entering, let alone bikers.