No Jack, they arent necessarily. 3D props do give a lower top speed and help in braking. But trainers need some amount of forward speed for flying. Granted trainers can fly very slow and the 3D props help in braking on final approach, but this can cause a stall just as easily if the inexperience pilot isint careful.

Also, since you have less air speed, you dont have options if something goes wrong. For example, if you are going at a good rate in a trainer when your engine quits, you can trade the air speed for height or vice versa and land dead stick. With a 3D prop, you lose part of that option.

I am now flying exclusively 3D airplanes with 4 and 5 pitch props. But back in my trainee days, I used 12x6 and 11x7 exclusively on my 55AX (I now use 13x4 on the same) and it helped me many times.

Ameyam