I ran a box stock LE issued M&P 9 in a class last weekend. I chose to use it instead of my PT.com M&P 9 because I haven't had a chance to put many rounds through it yet and nearly immediately forgot about it.
I realized late Sunday night that I hadn't my usual carry/training/competition gun. I didn't notice the lack of the Apex RAM, Pro sear, Mass trigger block, etc. while shooting from improvised positions, shooting at speed, or breaking 25 yd precise shots.
A surprising tidbit to me at least. The gun worked, I got my hits, and my times were representative of what I expect. Maybe all of this tweaky stuff isn't as important as I once thought it was.