Personally, I have to agree with Lockedon. I've always thought the bullet was squirrely and unpredictable. Even in an MP-5 (which is a great weapon) I don't like the bullet. I generally caried a "sawed off" 870 for entries (we didn't have M-4's yet and I HATED Styer AUG's.
I did use a USP in 9mm as a tactical handgun for two reasons. At the time, they (H&K - USP) were the leaders in intergating a lighiting system into the weapon frame. That is absolutely critical (in my book) in SWAT scenarios.
The second reason was, for some unexplained reason, even thought I didn't like the bullet, I could hit like a son-of-a bitch with it. And I was certain that if some asshole somehow got one of my guys, or a civilian, between me and him/her, he/she would be center punched right in the forehead 100 out of 100 times (at interior structure distances).
If you don't hit the target, or if you hit the WRONG target (God forbid), stopping power, etc., doesn't have much bearing in the argument.
In that respect, I even loved my MP more, in that I could tripple punch a three shot burst into a BG's forehead all day long, with one eyeball tied behind my back (don't try this at home).
Which is perfect in a guy's living room! But I wouldn't take one to Iraq. Actually I would TAKE one, but it would be a special assignment type of application thing.