I used a co-pilot to help me learn to fly R/C over a year and a half ago, and it worked well.
I would recommend the following, set the gain no higher than 50%, set the copilot up on the landing gear channel so you can turn it on and off during flight. do not fly inverted while using the co-pilot. FMA has a more sophisticated unit available now that can operate with dual aileron servos and rights itself from inverted flight by roll, a much better set up.