Expo seems to be as or more useful than dual rates.
Poking around, many models seem to have the high rate set at 100%, and the low rate at about 70-75%.
I'd favor a high expo at the high rate, and a lower one for low rate for initial setup . Say 40% high, and 20-30% low.
Setting up the servo centering and travel correctly is fairly important, and helps with such things as matching servos and reducing
peak currents, as well as improving resolution. Allowing control surfaces or servos to "hit the stops" is not really desired.