I have an HK45 and USP 45 and the HK45 is
vastly easier to shoot accurately for me. Both are hardcore reliable. I don't worry about 2 rds less (there are 13 rd extended mags for the HK45 if you are worried....but you'd be better off practicing more instead). I like mine enough that I'll eventually get a Tactical version also, probably LEM. They are actually a STEAL considering what they are!
The ergo improvements on the HK45 are in another zip code. I do think it would be easy enough for HK to develop a slightly extended 12 rd factory mag, and they SHOULD do this, although apparently they hate their civilian customers. It is still a huge firearm, but much slimmer than the USP, which makes it a viable CCW option. It carries as well as a full size 1911. Works very nicely in winter, especially in a Kirkpatrick leather shoulder holster for roadtrips.