The 40c is directly comparable to the Glock 27, not the Glock 23. There are several M&P40c threads here already. Some searching around will give you some good reading material.
As to the safety, draw your own conclusions. If an agency mandates it, and S&W wants to sell, they have to make it, but a private owner can pick whatever suits him. He trains only himself, and he can establish whatever level of competence he is willing to obtain.
Generally, I have a strong preference for a thumb safety on an autoloader, owing to a lengthy 1911 background. Unfortunately, now that I have a few M&Ps, trading them off and getting safety-equipped versions would be expensive. (A problem for me, not for a new purchaser. It would be nice if the factory would offer a retrofit, at a reasonable cost.) Since I do not want some of my guns working one way, and others, another, the last M&P I purchased continued the pattern of without safety, even though I normally would have leaned the other way.
Pick up an M&P with the thumb safety and see what you think. I have seen a few guns that the action of the safety failed to inspire any confidence. The safety moved from safe to fire with way too much ease, and did not have the positive feel that I am used to in a 1911. The safety does tend to interfere with the smooth side design of the M&P, but admittedly, to a minimal degree.
