(This is an OLD thread....)
I have an M&P9C, an M&P40C, and an M&P40FS. The 9C's got a thumb safety.
I took it because the dealer had only the one gun, and being a 1911 guy, swiping off the safety is habitual. (I always carry a 1911 in Condition One, AKA "Cocked & Locked".)
What I found is that the thumb safety on the 9C is just too soft to protect anybody from anything. While it's not too likely to move by itself, holster contact IMHO
might do it, or just accidental finger contact in handling. IOW, I don't trust the thing.
The silly little safety in the trigger is a joke, IMHO, too, although it
may help as a drop safety. The real drop safety in the rear of the slide is going to be a lot more useful.
I gave the gun to my daughter. She also knows how to work the thumb safety, and doesn't carry the thing - "nightstand". Can't talk her into getting licensed, and her employer won't let her bring it to work anyway.
Now, I'm told - I haven't got one yet - the thumb safety on the Shield is pretty difficult to turn on or off, and may be a better "childproofing" option. For the guy who puts one in his pocket, though, you'd better practice turning it off.... IMHO, the one on the 9C wouldn't stop a kid over about 2 years old....
Now, if you have one of the other S&W guns (or just about anybody else's) where the lever position is reversed (i.e., "up to fire"), like my old M39, being a 1911 guy puts you at a disadvantage. You can carry the thing with the safety off if desired (that defeats the drop safety in mine), but trying to figure out whether the gun in your hand wants the lever up or down can be a problem....
All of that said, pick one you like, and train up on it to the point that you do it automatically. I'm at the point where I try to flip the safety on or off while handling one of the M&P's, even though there's no lever there. I'm just used to the 1911....
(I carry a small 1911 "outdoors", and the M&P40C or FS "indoors". The reason being that the M&P's are very light, and don't require a special belt. Goes well with grubbies
.... On a trip involving aircraft - i.e., checking a weapon - it's one of the 40's, though. Never check a gun you really want....)
Regards,