Mine are the KCI drum mags, jamming occurred 2 times when started from a full magazine. After that happened I threw it back in my bag and used 30 round mags and decided the reload was quicker than messing around with a jam from the 50 round mag.
I just got my MBX Mega last week.
Not sure about selling it, gonna mess around with it for a bit and see if I can get it ironed out.