When I considered buying this item for my new M&P40c, I could not find any reviews from someone who actually had it. I decided to get it and post a quick review for anyone else looking for one. Setup was amazingly easy. Literally from in the box to functional and on the gun in under 2 minutes. Pop the batteries in place and change it like any of the interchangable backstraps that come with the M&P. Then all you have to do is adjust it to the distance you want (came zeroed for 50 feet). It works pefectly, exactly like I expected it to. Very bright and can be seen even in most bright situations. It will actually light about 1/4 of my bedroom around the target hitting the wall with the lights off. I wouldn't hesitate to recommend it to anyone. It still fits perfectly into my Fobus holster. If you want to know if it will fit your holster, put the gun in your holster. The laser almost exaclty covers the serial number on your gun. If your serial number can be seen while holstered you should have 0 problems. I did have a Blackhawk CQC holster for a Glock 21 that fit both this gun and my Sigma (way to long for this gun actually though) that it interfeared with. The gun went in and holstered and functioned perfecly but the laser pushed the plastic out and rubbed on the inside (again where the serial # is). The only negatives I have found at all is that I do have to squeeze the grip slightly harder to activate the laser than I normally would. Maybe I have a normally soft grip and this won't be a problem for you. It's not really a problem for me either, and I have found that even with my normal softer grip the laser activates as I apply pressure to the trigger (causing me to squeeze harder). This can actually be a nice thing as I can have a grip on the weapon without necessarily activating the laser. Simply squeeze harder and it will activate. And I have no doubt that in a pressure shooting situation my grip would easily activate the laser. It can also be easily turned off altogether with the master button allowing you to still use your iron sights to practice (to be ready in the case of some unforseen failure when the laser is actually needed). The only other thing I can say is that the advertising says it closely matches the medium grip that comes with the gun. I had used the medium grip since I bought the gun, since I was planning on getting this. That said, it feels more like the large grip to me. Not much difference but it felt slightly larger than the medium grip, but I quickly adjusted to the difference. Bottom line....Buy it you wont be disappointed. I found it for $230 (not here) and don't regret the purchase one bit. Go for it.