Well I had a few problems with the P-12, and the HK had certain advantages over it in my opinion. Roughly they are as follows:
1) P-12 mag release would engage if you leaned on the gun a certain way; HK design prevents this (I had to shift grip on P-12 as well to engage
2) P-12 was basically unreliable; it was not a limited edition
3) I like being able to carry hammer down, safety off
4) Calibers are the same
5) Similarity to 1911 control style permits continuity of training
6) Decock is a handy feature, and lets you safetly decock
7) Grip safety on 1911 styles is a stupid feature in my opinion, sometimes it won't engage properly and that's a real tactical nightmare
8) Trigger pull is probably inferior to 1911, but like any trigger can be mastered.
My $.02 [:D]
8)