RE: Why need low wing trainer?
A pattern plane is designed to fly a predictable manner, so they are not particularly difficult to fly. One thing is that they are not self-correcting.
I started my flying on a high wing electric foamy with ailerons and it got easy to fly. Then I moved up to a "pattern style" foamy (GWS Formosa). It was a pretty big step. The plane goes where I point it, but my system (brain and fingers) did not immediately know how to point it where I want it to go...
Competition level 2m pattern planes are not cheap. The first low wing should probably be something that will not break you heart and bank in case of a total loss.