Permanent polymer pic rails (though the top rail can be replaced by an armored, yet it’s still interfacing with a polymer receiver) are a liability for both durability and precise optics zeroing. Plastic may prove fine for a police gun but the Army would have to implement this as a military subgun. There’s a reason classic military subguns are built like a tank.
There’s been questions from hard use owners about the durability of the CZ EVOs plastic feed lips in its translucent plastic mag. Compare these to UZI or MP5 mags and remember the US Army intends to adopt a military subgun.
The controls are HK-like but user testing has noted a design flaw in the current models where the safety interferes with hand coordination. CZ rushed out a temporary fix and then realized the expedient solution wasn’t ambidextrous. That’s a problem indicative of unsatisfactory real world testing that might not have gotten out of the design phase at Hk.
Finally the CZ is designed as a straight blowback subgun. This means implementing a heavy bolt group and a lot of reciprocating weight. That’s fine on the slow-firing much heavier UZI but the CZ is very light weight being made almost entirely of polymer. The CZ has a fairly high cyclic rate. Users have reported shot-to-shot accuracy issues in all select fire modes. There is also a question of gas and debris blowback to the user in a high cyclic straight blowback design when suppressed. The US Army is still going to be beholden to 124-grain NATO spec 9mm which is fairly hot and gassy in my experience. The MP5 has some gas venting from the chamber but it’s delayed roller lock action does mitigate it fairly well.
I’m sure the CZ is good but it’s high plastic construction for lightness isn’t the most important positive attribute for rugged military use. The design issues with CZ realizing problems after release is not very Hk-like to be honest.
There’s no other subgun (including the Hk MP5) as reliably battle tested as the rugged slow cyclic rate UZI. There’s no subgun as surgically precise as the Hk MP5. I think the US Army should examine the positive traits of both of those designs before they adopt a modern subgun. The CZ Evo doesn’t yet match the best traits of either of those elder subguns.