The problem with a weak engine and a low pitch prop is that you won't be able to power through the wind. That can be a fatal flaw for a beginning pilot. If you only fly in 5 mph wind or less, the weak engine will pull the trainer around just fine. But where I fly, that's a pretty rare thing. It's pretty standard in windy places to put a good ball bearing .46 on trainers just so you can get your airspeed up enough to not get tossed around all over the sky.