Thank you Hammer -
1) I have a budget in mind but want to see what the overall feedback is on the 3 guns to see if the MPX-K is worth the extra $
2) Looking for a short barrel (8" max) and folding brace
3) 9 mm for sure
Ok, that's helpful. I have a Scorpion Evo S1 pistol - 7.75" barrel with a SB Tactical folding brace. Overall length with the brace folded is about 16.5". It has been absolutely rock solid with over 1200 rounds of various ammo without a single malfunction that I can recall. I got mine for sub-$800 and put a few hundred into upgrading the trigger, grip, etc + light & RDS.
I have also shot the MPX carbine, and it is extremely soft-shooting compared to any direct blowback system. Whether that's important really depends on the shooter. For me, shooting 9mm out of a direct blowback gun that weights 6 lbs, I don't find the recoil to be an issue at all, but YMMV. I
do think you pay a fair bit more for that softer-shooting MPX platform, and it adds more complexity than a direct blowback platform like the Scorpion, which couldn't be much simpler to take apart, clean and maintain.
One possible advantage to the MPX is that it is essentially an AR platform, with the same controls. So if you want something you can train with that is consistent with an AR, then the MPX would be the choice. The Scorpion has a different manual of arms, more akin to MP/SP5 in terms of charging handle location, mag release, etc. For me, I don't find that switching back and forth between the two is that big of a deal, but I know some people want to have one consistent platform across multiple guns/calibers.
My only other thought is that I don't see much of an advantage to going with a really short barrel on a PCC (3-4") - you're not really gaining much over just using a handgun except a little more stability, and you're really getting into a weapon for very niche application, once you put the "cool factor" aside. I think that 7-8" barrel is ideal.