I currently carry a fs M&P9 as my duty pistol and i just recently sold the first M&P9 that i had for two years. Both had Apex DCAEK kits installed. The pistol is fantastic, except i am convinced its accuracy is lacking past 15yds. I have shot it from a solid supported postion on several occasions as have many other more accomplished shooters than myself, and both of my M&P9's would only hold about a 6" group @ 25yds.
I have heard identical accuracy reports from several other well known M&P9 shooters who have vast experience with the platform.
My M&P45's were far more accurate for me @ 25yds.