I got an M&P40c last year as a possible carry gun (I also have a SIG 229 and a Ruger SR40c for the purpose). The trigger was mushy compared to my others, but a lot of dry-firing either finally defined the break or I got used to it. That, together with no failures in an admittedly low round count, sees me keeping the gun.
What bugged me from the get-go are the stock three-dot sights. They are quite good with enough light, but self-defense is often undertaken in low-light or the dark.
I replaced the stock sights with XS Sight Systems' Big Dot Tritium Express. Lay that fast-acquired well-illuminated puppy on any threat within three yards and you are bound to hit it. That's the philosophy behind it.
But as experienced shooters almost uniformly say, if you can't hit your target 3 yards and in by simple point-shooting, you need to practice.
Moreover, the Big Dot was taking the fun out of shooting for me. I couldn't get a tight group at 10 yards, what with the enormous Big Dot covering what I was trying to hit. The Big Dot had turned my M&P40c into a dedicated self-defense gun. I'd lost the entertaining option of quick and precise shooting at paper.
Having put Trijicon's HD Night Sights on my SIG 229 and SIG 220, I see they are better suited to my needs than the Big Dot. I can find the smaller front sight in all light conditions, great for self-defense farther out than 3 yards, and never confuse that sight with the rear sight's barely noticeable two dots in daylight, or unnecessarily obscure a bullseye with a front sight too big.
I expect to like the result, but thought you might want to consider this aspect in your selection (although the date of my response is probably too late...).
Doubting groupthink since 1984.