OK i read these comment have will shed some light on things. first i did give it 4 stars for the reason below. But fenix as a company hands down AWESOME customer service and great lights.
This advice is for Fenix... If you listen to your customers for anything this would be the one thing to listen too.. I love the mlock mount, but you really need to adjust one thing for it to be perfect. GET RID OF THE ROLLER lock thing and use proper Mlok Fasteners where they have to be locked in with a allen key.... Youd have yourself a home run with it.... guns = vibrations and roller things meant for use with fingers dont stay locked in.. see pic below those are proper mlok screws.
Id be more then happy to test one with true mlok bolts for you and give you my honest unbiased feed back as a normal person and not some youtube person etc. You may also want to think about maybe adding a pica-tinny rail mount also for those needing that option, You have that option for pressure pad mounts..... But again it would also need a adjustable pic bolt.
My light of choice was the uc35. When placing the uc35 in the rings remember you can remove the battery cap and the body unscrews from the head thus allowing you to slide in in nice and easy without having the rubber messing things up. yes i could have used my pd36r pro for the brightest light but I dont see a need for anything over 1000 lumens on a firearm if i need more ill pull out something strong.
Now for those saying they couldn't get the mlok tight enough i was in the same boat then it hit me a little allen key will fit into the holes on the roller which in turn will allow you to really smug it down BIG TIME. i have the same setup on two different weapons. I have not put it thru its paces yet on if it will last thru recoil. Worse case ill add some red loc tight....