There used to be someone on these forums who rode one regularly. He had a passion for riding the thing up-and-down hills.
Posted pics occasionally, too. Maybe he'll chime in if he sees this.
Me: I got one for free, 24: wheel model. It wasn't hard to get started and stay up on it, but to get good at it to where you'd feel comfortable on the road (turns, stops, backing up, avoiding others and things, etc) takes a lot of practice and I didn't stick with it.