Well, I have been carrying the M&P Shield 9 for about a week now in this holster so I will provide my thoughts.
Pros:
-Great price and very fast shipping
-Comes in a variety of colors/prints (if you're into that)
-Great retention and the gun clicks in place
-Slim and lightweight with minimal printing
-Rigid in the main body
-Easy to holster/unholster and grip gun
-Nice smoothed edges
-Very comfortable for a single clip IWB in Kydex
Cons:
-Belt clip is a little flimsy (can aid in flexibility during movement)
-Not adjustable, has fixed cant
-Has some gaps around the seam
-Not as comfortable as a hybrid holster
-Not as sturdy as some high-end Kydex holsters
-Limited to specific gun models but the selection is growing quickly
Cook's has great customer service and the turn around is fast. From the day I ordered the holster to the day I received it was 3 days (Georgia to Texas). That is quick. It does not have the bells and whistles of other Kydex holsters such as replaceable belt clips/loops and it is not adjustable for cant or position.
The main benefit of the holster for me is that it is minimalist, lightweight, thin and great for summer carry. While the corners can sometimes dig at you, all of the edges have been smoothed and polished making it less noticeable and more comfortable. I carried this all day for a week and found it to be more comfortable than my leather holster (likely due to the thickness).
Overall, this is a winner and I will keep it for daily carry. For $45.00 shipped, shipped quickly I might add, this is a great low cost option. Cook's offers this holster for a variety of handguns and they said more guns will be added to the list soon. This holster comes in at about $20-30 less than most of the other options and is effective. I can't comment on long-term reliability yet but it has taken a beating this last week and held up well. Mag pouches are available and they also make other items by request including money clips and phone docks.