A person I'm very familiar with was actually in Delta. We went to his retirement at Ft. Bragg, at the Delta headquarters building.
He took us on a small tour, which was not allowed. The building is shoebox-shaped, and on a hill. The front has a door/reception, right in the middle, at ground level. All along that side are conference rooms and such, in one long row. Some rooms have a door in the back, that leads to a walkway sort of thing, which runs about down the middle of the long axis. The walkway looks out onto a lower floor, with loading docks, workshops, cranes, etc. On that lower floor, outside, is a small memorial garden, with a wall that has all the names of fallen Delta members.
Anyway, along the wall of that walkway (the wall shared with the conference rooms' back) there are display cases, big plexi things kinda/sorta mounted to the wall. One has the blood-stained uniform Manuel Noriega was wearing when he was taken prisoner, as well as a 1911 with his initials in the grips. Another has satcom gear and electronic stuff (including an umbrella with cowboy chrome painted on the inside), another has a door from a humvee that has lots of spalling from an RPG hit it took when it was attached to a vehicle in Somalia.
Another case has every personal weapon Delta has fielded. There's a Thompson, a grease gun, a BAR, and more modern weapons in it as well. I asked him which was his favorite. He pointed to the MP5K, then did a little sort of pantomime of him pointing, shooting, crouching, pointing again, and so on. Then he said, "It's small, light, reliable, and you just can't really seem to miss." And that was that. Then we moved on and looked at his old shop.
So I'm going to take his word for it over woohoocollapse's that the MP5K is just fine for its intended purpose.