It is a soft plastic motor mount. It has not the strength needed to handle a minor crash or a powerful motor.
I had one on the sport cub and ti cracked with no hard landing or similar, just plastic fatigue. It began with white lines from each motor screw to the near ones and then (on flight) cracked. luckily no damage to report except the mount because the plane flies great it is a "floater". It was the second flight of the plane with the mount, so it was no old plastic also.
It would be great to have a better plastic motor mount or an alloy one like the ones that sells "CustomsRC".
I did not use the stock motor, i put a NTM on it with a little more power and the plane flies with 4 cell 2200mah, even i have not pushed it, it could float at half throttle or a little more.