I have to admit that I am a Sig man - I think the Sig 226 may be the most reliable fighting handgun ever made. But, about 4 or 5 months ago, I bought an H&K USP in 9mm and it's really starting to grow on me.
The trigger is just a bit gritty and heavy in DA. I replaced the stock hammer spring with a Wolfe reduced power spring; I think I went from 16# (stock) to 14#. This was against the advice of Wofe Gunsprings for a carry gun I should add. But, I shoot about 200 rounds a week and fire a magazine of my carry ammo anytime I make a change to the gun and fire about a box of carry ammo about once a month, just to be sure. The reduced hammer spring made a significant difference; it's not a match trigger job by any means but it did reduce the DA trigger pull.
I think the SA trigger is wonderful! It's short, crisp, smooth, and breaks at 4.25#. But if that were all there was, I wouldn't be much impressed; my Sigs are all that and more. But I began to notice things about the USP. Like after a reload, the slide barely has to be moved to release the slide lock and chamber a round. Again, not a biggy, but different enough to catch my notice of it.
Then there's the mag release, first, it's fully ambidextrious. Second it's weird, but once I got used to it, my other guns seemed, well, awkward. You know how you have to change your grip to reach the mag release with your thumb on many guns? Not so with the USP; you just have to move your trigger finger to the rear of trigger and press down on the mag release - it works! I have to admit I like it much better than the conventional thumb buttons.
I'm usually not big on safeties, but the USP safety/decocker thingy, adds a lot of versatility, at least for me. I can carry the gun in DA/SA with the safety on or off - my preference. I can carry the gun cocked and locked with the safety on just like a 1911. In fact, the thumb safety is in the same place and orientation as a 1911. If I need to take the the gun out of the holster for administrative duties, like going to the bathroom, I can engage the safety, remove the gun and it's just an added precaution. The same is true if I need to take the gun out of the holster in the car, say to go into a post office or anyplace where the gun is inappropriate. I can engage the safety, remove the gun from the holster, place it under the seat or in the glove box without worrying about the trigger hanging on something and...
The gun looks big, but seems to carry small. The grip fits my hand comfortably and the USP is light. Including empty magazines in each gun, the USP is only 2.8 oz heavier than a gen 2 Glock 17, 4.5 oz lighter than a Sig 226, and 4.2 oz lighter than a Sig 229. I suspect if I could have compared the USP to a gen 3 Glock 17, the weights would be even closer.
Slide/frame widths: G-17 = 1.15" (The frame is actually wider than the slide), Sig 229 = 1.12", Sig 226 = 1.0", USP = 1.134". So, the USP slide is only 0.016" wider than a G-17!
Grip widths: G-17 = 1.16", Sig 226 = 1.31, Sig 229 = 1.25, USP = 1.21. So the USP's grip is only 0.05" wider than the G-17. That's less than a sixteenth of an inch.
Overall dimensions: the G-17, Sig 226, and USP are essentially the same size.
So the USP isn't such a big gun as you may think! I know it sure carrys good, being so light. And of course it conceals just as well as a G-17, Sig 226, or 1911.
One downside of the gun is that stupid accessory rail that none of the Picatinny stuff will fit. That's a real disappointment on such an otherwise fine gun. And, the mags are kinda big, but then I think Glock mags are wide too and the USP mags are only 0.03" wider than a Glock mag.
Most importantly by far, the USP has been 100% reliable. And far FUNNER than I ever imagined. I got all the confidence in the world in this gun.