FWIW, I actually tried to order my second M&P with the magazine safety ... (under the armorer discount purchase program, hence not going to find one at a retail store) ... but when I called back to check on the availability of the model configuration I wanted, I was told the current production run under way was made up of models without the mag safety. I decided to take one without the safety rather than wait perhaps up to a couple of more months.
The M&P magazine safety is elegantly simple in design and function. A steel lever and a spring. Much simpler and more robust than the design used in the 3rd gen guns, in my opinion.
It wouldn't bother me at all to have the mag safety in a M&P pistol I owned and used.
I've carried many issued and personally-owned 3rd gen guns with mag safeties for 20 years without problems.