Shooting low can be corrected by shooting a heavier bullet if it's reasonable.
My M&P shot slightly to the left when I got it, about 3" at 25 yards. I adjusted the rear sight a couple weeks ago.
They are novaks and made of steel so I wasn't at all worried about whacking them with a brass punch.
Anyhow, first I had to use a torch on the set screw for a few seconds to break the loc-tite loose.
Then it took some pretty solid whacks to move the rear sight. Even if you somehow lost the screw the sights would probably still be solidly in there.
As for elevation, I wouldn't be too worried about it.
First, they're likely to be dead on to begin with.
Next, The sights are dovetailed in. You get one that shoots low, call S&W and complain, send it back, and it should come back fixed with the correct height front sight installed.
It sucks but it's a small issue to fix and not at all related to reliability. IIRC, they are one of the companies that will pay return shipping.
I did a lot of research on them and before I bought one. My friend who works at my favorite shop has two. S&W was doing a promo on them for awhile where if they sold like 300 guns they got a free one.
Consequently, they were selling a lot, he now has two of them. This guy could have sold them back to S&W but he kept them and carries one now. His wife has the other one. I asked him about them - he and the other guys at his store have sold thousands with only two returned - one because of faulty handloads. The competing gun store in town (where I bought mine b/c I wanted one without the mag disconnect) has sold even more, sells out of them almost as fast as they get them, and has yet to have any complaints.
I finally gave in after finding nothing bad written anywhere about them and I'm not at all disappointed. After a couple hundred more rounds and a decent Kydex holster mine will become a three season primary CCW.
After this one gets 1K through w/o issues I'm going to be wanting a second one.