I have owned a M&P 15 PS for over three years. It has the same piston as the Adams Arms setup. The rifle has exceeded my expectations and is not only the most accurate rifle I have ever owned, it is also one of the easiest to clean and maintain. I shoot mostly my own reloads and have never had a malfunction of any kind. It just runs great all the time. One of the complaints I hear is that a piston rifle weighs more, and therefore must be more difficult to shoot. I weighed my end cap, piston rod and spring and it came in at a mere 6 ounces. Some of the lights, lasers, bayonets, etc. that I have seen added on weigh considerably more than that. I recently added a Magpul hand guard and it fit just fine. The downside to the piston rifle is that I have become lazy in cleaning it because frankly the BCG just doesn't get dirty. There is powder residue in the area of the gas block, but it simply wipes clean with a rag and Hoppe's 9. Most people that criticize a piston rifle have never even shot one, mush less cleaned one. Given that almost all AR manufacturers now have a piston rifle in their inventory I am totally satisfied with my choice.