The Thera--Bands are OK at 230-250 Watts and have even been taken higher. No problems at all. Here is an APC 13 X 8 on 90 gram motor.
There are two bands on that prop, one will keep it on and the second is for some extra security. That is a quiet, well-balanced, prop running on properly installed prop saver. And that was at a bout 200 Watts peak there.
I am smart enough to stay out of the way and keep my fingers out of the action. If the bands both broke simultaneously the prop would walk straight up, slow, and then clatter to the floor.