I've never had a production light with QTC, but I played with modding a light with some, and like everyone says, it just seems like pretty touchy stuff that wears out quickly. It's fun to play with, but I don't think I could really count on a light to perform reliably with it. However, I won't be surprised if it does surpass magnetic control after a few years, if people keep working to develop the stuff into something more durable and reliable. It's much simpler than a magnetic ring setup, and could be implemented using much less space.
As for what control ring lights to look at, I've got several from SWM and they're all great. My EDC right now is V11R w/ HCRI emitter and a AA extender, and the control ring is the reason it's my EDC. The only thing that occasionally subs in for it is my EYE10 from Niteye, which I understand was pretty similar to the Jetbeam RRT-01. My EYE10 however has no detents, and the low can go all the way down to so low you can barely see it in a completely dark room, pointing it right at your face. This is the light I used most when my kids were infants, for checking on them or going in their rooms at night without waking them up. It really can go as low as anybody could possibly ask for.