Definitely my favorite aero engines, just the right amount of smoothness and power for a 5" quad. The bell is very strong but I had a small issue with 4 motor bolts stripping threads after an accident. iFlight was more than generous in replacing the motor and reassured me that it shouldn't happen. I'm more than happy to give these engines another try because they fly so well. You must try these engines at least once in your life, you won't be disappointed π€