Those are great, and offer a real workout. I have one that generates electricity that powers some blue LEDs. In a dark room, it very much brings to mind the image of something out of DragonBallZ or some science fiction film where people build up power charges in their hand and fire lightning at each other.
Except that when I throw it, Lukster's magical force grabs it and makes it orbit in a circle in the middle of the room. That's always embarassing.