I had a pair of ATC200S. I bought them brand new for $1056 each. They were my first big purchase ever. (my cars never cost more than $1000)
Are they dangerous, yes! Are they fun to ride? YES!
They are actually a little more maneuverable than a quad. They will go some places that a quad won't.
They suck in loose sand and snow deeper than about 4 inches because the front tire has too much weight. If spread over two wheels it's better.
They're easy to pop a wheelie and if you learn how you can pop one and land on your back, completely unharmed.
Don't turn the wheel if you're moving backwards and expect to stay on. You won't.
Don't brake hard and turn the front wheel. You will become a jumbled up mess with the 255# trike.
If you feel like you're going to flip when turning, resist the urge to put your foot down. It hurts when you run over your leg.
I flipped my ATC no less than 50 times and I don't have any permanent injuries. Most of the time when I flipped it it was, sort of, on purpose.
I did get a knee injury one one. I don't think it was because it was a 3 wheeler. I think jumping it just aggravated an older injury. My knee is still messed up.
All in all, they were tons of fun. When they stopped making 3 wheelers it kind of bummed me out.
And the reason they stopped making them, I was told back in the day, was the government outlawed them because they were considered dangerous. I don't know how the Can-Am trikes got past that, though. Maybe they have a differential whereas the ATC had a fixed axle.