i ran a HALO quad for a long time and it never caused the gun to malfunction, my only complaint was how much extra weight it ended up adding to the front end, made the gun very slow in fast target aquisition. i sold it off put the original handguards back on and now run an ultimak rail across the top with a burris fast fire II, it is super fast and light ad i love it. also have handled the surefire and tapco on buddies guns and both were fine and neve caused any issues, though the surefire is by far the more comfortable and better looking IMO.