dual rates are use full if you have someone eles that flys the plane, you can reduce the control surfaces when they fly and you can put them back to full when you fly just with the switch. also with the cub you do not need expo, it makes the servos less sensitive around center stick so its easier to control fast planes.
It does depend on which holes you use on the control horns/servos. I have mine connected to provide maximum throw, and hence use a bit of DR and expo on one switch setting for each control, to soften the amount of control surface throw when required and to provide a bit more scale flight characteristics. I'll PM you the settings I have when I have my radio to hand, as I'm at work ATM. I also found that I needed to adjust the throttle throw as at default the input from zero to WOT was a tiny movement. Quite scary during the first flight. I now have full stick movement allowing gradual throttle increase/decrease. I suppose this may or may not be necessary for you, depending on your motor and ESC. I'll add a bit in the PM about this too.