A few random thoughts...
You may like the idea of an external manual safety but I would strongly advise against it. I just saw a video the other day of a jewelry store owner who had a concealed pistol. A thug pulled out a gun and started shooting at the shop owner. The shop owner was already suspicious so when the bad guy went for his gun, the shop owner went to draw his as was only a 1-2 seconds behind. The problem was the shop owner's pistol had a manual safety that was engaged and the shop owner was not able to disengage quickly enough. Result? The shop owner never got off a single shot but did get shot himself multiple times. The only reason why he survived was that by the end, with the thug right up on him and the shop owner sitting there at his mercy begging for his life, the thug went to shoot him point blank in the head but luckily he was out of ammo.
Now you could make the very reasonable argument that the owner simply didn't train enough with his pistol and if he had, the manual safety wouldn't have been an issue. True, but it can be just as easily argued that with proper training and mindset, there is no need for a manual safety to start with. Whatever you get, you need to train with that pistol often and know it, and how to safely and effectively deploy it, just as instinctively as you know how to walk or crap.
Pros and Cons aside, are you sure the M&P9c is available now with a manual thumb safety? I know that was supposed to be an option at some point but the last thing I've heard was the only M&P's currently available with a thumb safety are the .45ACP versions?
Now, to the root of your question.. Yes, the M&P9c is a very good CCW weapon. The only downside to it IMO is the availability of quality fitted holsters made for it. If you already CCW now and have a favorite holster, check to see if that holster is available fitted for the M&P9c? If so, you should be GTG.