I had been wanting a light for an AR15 for some time now. After shopping for the past couple months I decided on the Olight M20S for its combination of battery life and lumen output. Here are the numbers: Low: 9 lm (150hrs) Med: 110lm (12hrs) Hi/Strobe: 320lm (~3.5hrs) I was impressed by the packaging of the bat. That first impression was carried through while continuing to open the foam lined hard case and handling the light itself. After a quick run to Walmart I returned with four CR123 batteries. Installation of the batteries was a breeze. Cycling through the four functions was made easy by a small button located towards the rear of the light on the side of the battery cap. The light comes with a belt/pocket clip which was removed before mounting. I played with different mounting locations but couldnt decide on a certain one. I chose on the top rail towards the left and on the right side. We'll see what works best after a range trip. I have two pressure switches on their way that will be capable of cycling through all functions. All things said I couldnt be happier with these two lights. They are super bright. Even the light bouncing off of the tv was uncomfortable when hitting my eyes. The strobe was intense as well. The performance is up there with any light I ever strapped on any issued weapon and the prices are awesome. In closing the only thing I can say I wasnt 100% with was the stock offset mount. Though it is perfectly functional and sturdy as heck it is a little bulky. But for the price of the mount you cant go wrong. When youre ready to purchase yours email - email@example.com , subject: Olight-GlockTalk This is where I got mine. Wendell ( bullit ) is a great guy who went out of his way to make me happy with my purchase. He even overnighted them so I could have them for the weekend.