I can't see impacts wrecking a rotor... otherwise alot more than your motor will be hurting; it would have to be a incredible forces to accomplish this. IMO
They are just crappy magnets.
“The modern astrophysical concept that ascribes the sun’s energy to thermonuclear reactions deep in the solar interior is contradicted by nearly every observable aspect of the sun.” —Ralph E. Juergens
I don't think the quality is very consistant regarding Feigao motors. I have one 8XL that I have been running in my brushless 1/8 scale buggy for over 60 hours total run time with no issues. I had another one come part in less than 30 minutes. Feigao motors are great for getting you into brushless on a budget but you bascially get what you pay for.