One thing for you to remember when listening to opinions here, specifically about reliability issues with the MPX. The Gen 3 is not a Gen 2 or a Gen 1. At a minimum, it has a different bolt carrier assembly, different gas port dimensions and a different barrel all of which play into the issues some had with the MPX. Put the most value on input from those with a Gen 3. That said if both are reliable as a rock I think the MPX is significantly better and I have a JP GMR in the safe as well. I have a Gen 2 and when I quit trying to find the perfect 125.1 PF load and just shot either factory or reloads at 140 PF or so I quit having problems and the gun still has far less dot bounce and recoil than any blowback. but again, this is with a Gen 2.