I much prefer expo to dual rates. That said, I wouldn't recommend either for training. A person should be taught to use finer, smoother movements. If they're going to grow as a pilot they'll need that fine sense of control, and many of the habbits we all have are set in place when we're first learning. Expo might seem like the easy way to help someone that's just banging the sticks, but I think it does them a disservice in the long run.