You will have to watch the video to find out.
The MP5 is among the most recognizable submachine guns on the planet and the definitive example of what some industry folk term the ‘3rd’ Generation of the submachine gun. The one where they turned into closed bolt specialized weapons instead of inexpensive stamped steel bullet hoses (‘2nd’ Gen) or elaborate heavy, woodstocked machines like the Thompson (‘1st’ Gen).
We are still in that 3rd Gen and I don’t believe we will ever pass beyond it. Oh, weapons like the MPX and Scorpion EVO3 S1 have made modest gains on the original MP5 for ergonomics but we are at an apex of pistol caliber weapon efficiency-in-role that is unlikely to be surpassed until a significant change and gain in ammunition is made.
We have the same plateau in 5.56x45mm weapons that we have in pistol caliber ones, the guns are built well and we are at the reasonable edges of ammunition efficiency so the change that is coming will be in ammunition.
The .300BLK “NotanH&KMP7” is and example of the problem. It’s a hybrid of the hyper compact MP7/P90 weapons in a conventional rifle caliber that works in a short barrel. It still isn’t a change of technology, which will be the next true leap, just an application of all the efficiencies we currently understand on our modern small arms. The weak point in this system will undoubtedly be how well the magazine works. Making the bolt and operating system work will be unlikely to pose the challenge that making sure feeding works will. But changing a rounds direction in the magazine is already something we have reliably accomplished in the aforementioned P90.
This cool new gun is a culmination of things we already know how to do, and do well, and the MP5k was one of the weapons that jump started this final subgun evolution cycle. The result has been a lot of weapons that work very well.