Want to pass on to anyone considering the Apex AEK Poly trigger -- this thing is superb. It turns the M&P into the pistol it should have been when it left the factory (well, along with the USB and the Apex Sear).
I have no connection to Apex Tactical, but don't mind recommending their product at all. What a positive feel. Shorter trigger pull, much more solid trigger.
I regret that I've had to spend about $150 on Apex parts to bring my $450 M&P9 up to top standards -- but it is still a cheaper than a Sig, H&K, etc., and every bit as good. If not better.
Thanks Randy & Co for your excellent products.