I can understand where the OP is coming from. From 2005-2013 I shot Glocks (19/17) exclusively in regards to handguns. However, when I knew that I was starting the police academy, in an agency that issues M&P’s, I bought a 9mm M&P and began to train with it. I continued to train with it exclusively until I shot top gun in the academy and got sworn in. From that day forward, I carry an M&P on duty because that is what I have to carry, and use Glock handguns for everything else (home defense, CCW, etc). I ended up selling the M&P that I used to learn the M&P line of pistols. When we traded in our old M&Ps for the new ones I did buy my old one from the department for sentimental value reasons only. I figured I shot top gun with it, and it was my first duty gun, so why not.
I shoot M&Ps just fine and have no issue switching back and forth. I also have nothing negative to say about the reliability of the M&P for the amount of rounds that I have fired through them. However, I prefer Glocks . Therefore, when I have a choice, I carry Glocks. I have way more time behind a glock, and a lot more rounds fired in Glock handguns.