Everyone makes a lemon
I'm a big fan of S&W since I began shooting. M&P 9 Full Size was my first semi-auto. The only flaw I've experienced with it, is an occasional slide stutter upon return. It has happened only a couple handfuls of times in 4 years and never resulted in any firing, feeding or ejection issues. M&P 9C & 40C both have been totally reliable/flawless and more accurate than I had expected. I load mixed brand and types of ammo in mags, to try and create feed or eject issues and it hasn't happened. I actually like shooting the 40 better than the 9's. When I began shooting people said stay away from the 40S&W, go 9mm or 45acp. So I listened to them. My favorite carry caliber is the 40 or 45 and typically it is the Kahr MK40. Now that I have a Shield 40, I will likely carry that when I want a lighter weight gun (about 5oz less than the MK40).
My S&W Lemon was the BG380 w/laser. Sent it in 3x's, but they could not get the laser to actuate from both sides with fingertip pressure as it should. They even replaced the frame and it still only worked on one side properly. The lemon law concept worked, they bought it back. Other than that, the only other issues I've experienced with S&W products are with revolvers. I had two firearms that had poorly pinned front sights. Both were considerably powerful weapons. A model 632 327magnum (first year) and a 460V. Within the first 25 rounds fired, the front sight disappeared! Yep, gone, nowhere to be found. From initial email contact regarding the issue, to received and repaired, I'd say it was roughly 2 to 2 1/2 weeks. Neither has had a repeat of the initial issue.