I agree with everyone that expo should be left for the more "seasoned" pilot, allowing the students to gain familiarity with the normal feel of Tx stick control. I prefere to run -40% on my Futaba radios because I like my throws set up on the radical side. Expo tames down those throws around center, until I want to unleash their power at the extremes. Also allows more "flair" feel/control on landings.