All M&Ps have a striker block safety. The striker block safety has nothing to do with the trigger 'safety'. The striker block safety is in the slide. It simply prevents the striker from breaking the breechface until it is moved up and out of the way via the trigger bar. Basically, unless the trigger bar is pulled back (via the trigger) into the firing position, the striker is blocked from moving forward enough to discharge a round by the striker block.
It really helps to understand how whatever pistol you're choosing to purchase/carry works. The XD pistols, for example, also have a striker block safety. However, the XD pistols use two other safeties not found on the M&P: the sear shelf safety and the grip safety.
I used to not like the M&P because of its use of a simple spring sear instead of a more "Glock like" one piece trigger bar with attached 'sear' and the sear shelf. Over time, I've grown to like the M&P more and they are currently the only type of striker fired handguns I own.
My M&Ps all have thumb safeties, but the thing to remember about the M&P thumb safety is that all it's doing is preventing the trigger from being pulled back far enough to engage the sear. It does not prevent racking of the slide or movement of the sear in anyway. Therefore, the thumb safety is simply a personal preference item for the M&P pistol owner.
It really helps to know how your pistol functions. The M&P is a dead simple design. Watch some videos on youtube to get yourself a better understanding of the different firing methods used by various striker fired pistol makers (e.g. Glock, S&W, Springfield).
