If you enjoy shooting, including pistols chambered in .40 S&W, and the price seems good to you, it's not like the compact 99 series is a
bad choice.
FWIW, the M&P 40c seems to offer a bit more in the way of controllability,
for me, but that might just be due to the subtly different profile and softness of the M&P's grip inserts compared to the ones used in the 99 series.
I really like my SW999c, BTW. One of my favorite small pistols. A friend of mine bought the SW9940c, and he also likes it quite a bit. He's fired many thousands of rounds through his since buying it. The only thing he complains about is when an old wrist injury in his strong hand flares up, and the felt recoil of the SW9940c is just enough to aggravate it. His 9's don't seem to cause him that problem, though.