I use the open top double for my 17. I love it. Be advised though, the doubles can only be worn in the vertical position ( at least this is the way it used to be). They are so slim that a horizontal slot will not fit on the back. The triples can be worn horizontal.
I have been told that the ones for the 9mm and .40 Sigma will fit the M&P 's in those calibers. However, i cant confirm that.
I have been told that the ones for the 9mm and .40 Sigma will fit the M&P 's in those calibers. However, i cant confirm that.