To the OP. If your Glock 26 and 19 are reliable shooters I would not trade either of them for the M&P 9. I own the 26, 19 (Gen 3's ) and a Gen 4 G17 they are extremely reliable firearms.
I also own a M&P9C and it has been a great pistol as well, but I like my Glocks better. I am one of the few that likes the feel of the Glock grip better than the M&P's. My M&P9C always feels like it will slip out of my hand. Whereas the Glocks lock into my hand much better. It must be that Glock hump or something.
I think you will end up regretting the trade.