Bangkok: The way the copperpaint works is, the root tip reaches the paint, it then tries to absorb the paint, the paint terminates the tip the way air would, and the hairy roots grow out of the main roots. If you don't entirely coat the inside the root tips may grow to where there's no paint. I coat the inside well and according to the Microkote folks, you can resuse the same pot again, the paint doesn't "wash out".
Triloba Tracker: I would recommend you switch ... It's been more economical to buy pots, even decorative pots, paint them and enjoy the same root pruning. I'm not in any way affiliated, just a happy customer, and would recommend to all my friends here switch too ...