I have never personally tried one. I did however call / email (don't remember) the mikmar company and they sent me some WONDERFUL DVD's about their company and how the bit came to be. If I had a couple hundred to toss around I would have bought one. I'm too cheep.
Should I ever come across a used one I will snap it up in a heartbeat. They work really well from what I can tell. The nose rope keeps you out of the horse's mouth too much and the bit keeps you off the nose. It works like a race starters count. On your mark (horse notices movement of the reins) Get set (horse feels nose pressure) GO (bit engages)
Hope that made sence to you. I'd go to mikmar.com and order the dvd. Its free and could answer more questions than I can.