I just had my second short range session with an M&P 9, Pro 5 inch, with a 4 pound FSS trigger installed by Randy Lee. All I can say is, wow. Prior to yesterday, my first range session with the FSS trigger, I have never shot an open carry FASTest quicker than 4.3 seconds. Yesterday, I had a couple of 4.1's, and today, shot two below 4.0, including a clean run at 3.78. I also saw several FAST body splits at .19, where I have never had a FAST split below .22, with the Apex DC trigger, LEM or Glock trigger.
As a reference, earlier in the session, I shot a few FASTests with my 9mm P2000, as my buddy is just getting one, and my best time was 4.5, the results seemed much less consistent, and it took a lot more effort on my part to run the P2000 than the FSS M&P, with splits in the .25 range.
I think the FSS trigger, on an M&P without a thumb safety, maybe too short for my taste for carry in anything other than a strong side OWB holster, but should work fine with a thumb safety model.