I can see where it would be sidewalk legal, but not so much street legal. Golf carts that travel at 25mph are only legal on streets where the speed limit is 45mph or less. I wonder if this has the same restriction. Also, I didn't notice a license plate. Did I just miss that?
I suspect it's treated as an electric bicycle. They are limited to about 20 mph or so, but in most states don't have to be registered.
Does it balance itself side to side, or only front to back? At 20 mph it's not all that useful. Even if it is street legal, I would not consider it street safe. I don't want to be on a contraption that's open to getting knocked off when cars are going by at 40 mph (common on our 35-mph streets) and I can only go 20. OTOH, it's probably no less safe than a bicycle. (Which I do not ride in traffic!) It looks cool, though, for tooling around in low-speed areas.