"I agree with this post that agrees with that post?" LOL.
Maybe that's really the bottom line here. The SD9 is made really well. It feels good in the hand, and is easy to maintain. It's fun to shoot. The problem? If an armed BG came at me, I'd be afraid I'd miss if I had to shoot him with my SD9.
For me shooting anything is fun from a BB gun to a potato gun

BUT self defense is not about fun it is about survival & what works for you best. Mine used to be a shotgun, now it is #2.
If you would like to stay with S&W I would rent any M&P & give it a try. good luck.
& PS I looked into trading my SD9 in on the M&P40c & they would only give me 160 for it.