Yeah, the first dude who made one (the creepy-lookin' biker guy in the photo there) almost broke his neck in a crash on the prototype. It's apparently almost completely impossible to drive his original version. Maybe they came up with a cool gyro setup. Oh yeah, and it predates that southpark episode by years. I always assumed they based their joke on his devive.
Also that last pic there of the gyro unicycle fuel cell thing I remember it's made by the Bombardier corporation.
That biker guy is NOT the original inventor, not by a long shot. I've seen pictures of those type of vehicles that are old. As in, black and white pictures. The kind of black and white that are more reddish...sepia maybe?