The OM spiel is typical lawyer stuff. The PF9 is much less robust by comparison, but even Kel-Tec says it will withstand +P in limited use. I think the M&P will do just fine with +P ammo, as long as that's not all you shoot for thousands and thousands of rounds.
That said, for civilian use, I don't really see the point of going 9mm+P. If I want more power, it's much easier and safer to get a .40.
If you are LE and the dept mandates 9mm only, then maybe you would want to practice with regular ammo, then carry +P, like 38 special and 357.