Expo and Dual Rates are odds on the only two functions (aside from sub trim for setup and centering of servos) that will help re learning to fly any basic aircraft (the kill switch is only mandatory if you get a nitro model) ..... I can recommend that you remember and "really understand" what K.I.S.S. means - the flying bit is difficult enough to begin without worrying about all that other junk. Don't over complicate things unless you have too.
I use a Dx6i on my nitro heli, and sure you have to use a few of the programmable settings that are available, but in all fairness, even on that monster, the only thing aside from the gyro gain that helped to make that bird easier to fly was the expo adjustment, the rest of the TX's functions are really almost wasted on that model, and trust me when I say that a .50 nitro heli is a hell of a lot more complicated and harder to fly than a basic 4ch trainer plank (I now have one, so can knowingly comment on that front)