Not necessary to use dual rates on a trainer as they have smaller controll surfaces.
Fun fly planes ect., which have very large controll surfaces with extreme travel is where the advantage of dual rates comes in handy.
Without a way to govern the travel on the ailerons and elevator, youll tend to overcontroll during takeoffs and landings as well as flying squerrilly untill you get used to the plane.
Your next planes after the trainer will most likely benifit from using the computer radio, so, if you can start off with one, youll save $s.