I have used adjustable gas blocks from several reputable manufacturers. Of all I have used, the SLR Sentry series of gas blocks are the best all around in my opinion. Machining and finish is top notch. The clamp on version is simple to install, and I have had no issues with the block becoming misaligned, even after thousands of rounds. It is easy to adjust, and has positive clicks for each adjustment. I have had mine for about a year and I love it. I would definitely recommend this block to any shooters who are new to adjusting the gas impingement system in their AR-15.