The M6 is plastic with a plastic lens last I heard. The Streamlight is Aluminum with a glass lens. I have heard from a number of people that the M series of lights don't stay attatched to the pistol too well, and the lens accumulates carbon fouling that is difficult/impossible to remove.
A forum community dedicated to Smith & Wesson M&P Pistol owners and enthusiasts. Come join the discussion about optics, performance, gunsmithing, troubleshooting, reviews, accessories, classifieds, and more!