Good post. I just installed an APEX kit in my M&P .40 last night. I've never even taken a semi-auto down to that level, and didn't find the install difficult at all. The improvement was amazing, much lighter and crisper break. I tried it before doing the USB and was very happy how much it reduced the grittiness. The M&P trigger went from the worst in my collection, to the best that I have in a striker fired gun.
I have an XDM .45, the trigger is very nice for a stock gun, but I may consider the PRP in the future after shooting it a bit more.