> If you start out with 3 channels then you will probably need to be retrained when you go to 4 channels <

This is a joke, right? I have flown 1 channel, 2 channel, 3 channel and 4 channel planes and there wasn't any "retraining" involved. To turn, you move the right stick to one side and give a bit of up elevator. Exactly the same in 3 channels or 4 channels. The only real difference in a trainer is remembering which stick to use to steer with on the ground. Not a big deal, even if a senior citizen like myself forgets sometimes. (G)