I bought one of these (the smaller P30SK) from a friend about 6 months ago. It's a refined compact 9mm carry pistol, and has quickly become my favorite.
The heritage of H&K traces back to Mauser in Oberndorf where the founders had worked before founding the company.
I understand that the designers obsessed over the design of this fine hammer fired gun for a couple of years, making small changes constantly to improve it through it's design cycle.
You'll get used to the magazine release quickly. It's one of the best ambidextrous designs I've encountered.
Now, just don't let the unique rifling bother you. No, it's not worn. It's an advanced polygonal design.