The Model 659 is one model, but M&P can be a lot of different things: it is not just one thing. M&P (pistol) can be a 9mm, .40, .45, .380. The 659 is just a 9mm I believe, produced between 1982 - 1988.
Your model 659 is a second generation S&W Semi-Auto pistol. Subsequently (in the late 1980's) S&W came up with a third generation design family with a number of models (like the 5906, 6906, etc...) really variations on a theme for their metal framed pistols with lots of options and alternate calibers. Many of those went into police service.
When S&W came out with their first polymer framed pistols, they started using the "Military and Police" branding for them. In reality, every generation from the hand ejector revolvers of 1899 through today's polymer guns have been sold on contract to M&P organizations.
The full M&P line pistols are the only polymer S&W pistols that I would consider, including the full size, compact and Shield series. I am not very impressed with the "EZ" versions, and definitely don't recommend the Sigma or other cost reduced lines.