I've been around, and have seen a bunch of them... Interesting observations have included flying out a tank (several minutes) with no rotors, and coming in on the lines and wrapping several feet of .015's around the rotor post. They're unusual, but fall under the catagory of novelty at best. I've seen them used in Balloon bust because they tend to fly slow and stable.
Jim Lee built an Otto the Gyro on steroids, powered by a throttled large case Fox... .45 maybe? Rumor has that it has looped but I wouldn't recommend trying it.
I'm still looking for a shot of a complete (undamaged) Otto, I think this one is Jim's older Otto after balloon bust at some unknown contest... Maybe Omaha?
Edit: Added a second picture, I'm sure this one is from Omaha. There are two Otto's visible in this picture. The red one to the left belonged to Kirby Chilton, that's probably him in the red shirt working on it, the other person is most likely Todd Lee. The next Otto belonged to Brett Smith, again that's him working on it. Jim Lee is probably just trying to get out of the frame, and then the far right is Dad fueling my Skystreakishthing...
Both pictures are from about 93 or 94, and may not have been at the same contest.