Having been issued an HK MP5 for about 15 years and also having experience with Colt SMG’s the roller delayed is the superior system. We shot the HK MP5’s 4 times as much as the Colts and had almost zero issues
The Colts were problematic with anything but ball ammo and even then they didn’t run like the MP5’s did
And I say this as someone that shot the MP5 monthly on a team environment