I am in the process of getting one myself. For the M&P I found:
Blade-tech allows different mount options so you can always swap (Belt, Paddle, Tek-lok) and ability to add DOH
Models
Blade-Tech injection molded M&P special ($30) seems like it will work, but saw IRL it was thinner and a little flexible.
Blade-Tech "custom" kydex, I have not seen IRL but looks like thick kydex like Comp-tac
Comp-tac: These are molded specific to use and mount (including belt width) Makes for a strong product but reduces ability to adjust.
I used a straight drop Paddle one for M&P last week. It worked fine for IDPA, but I felt it would be nice to swap to DOH for USPSA in future. The kydex was very thick and strong.
I will be ordering the Blade-tech M&P for now with a Paddle mount and an extra DOH to swap it too.