Like other gas-forward devices, the Citadel's solid, cylindrical blast chamber and shroud focuses muzzle blast and noise down range away from the shooter's ears. It doesn’t actually dampen the sound in any way (like a sound suppressor) but the concussion is noticeably reduced for the individual pulling the trigger. While other gas-forward devices have wide openings the Citadel is enclosed and ported to tangibly reduce felt recoil.
I had the opportunity to shoot with the Citadel using an AR-15 chambered in .223/5.56 with a 16" barrel. The rifle was fired with and without the device in place. I could hear and feel about a 30 to 40 percent drop in noise and recoil from where I was sitting. It should be noted that the Citadel doesn't reduce muzzle flash. In fact, it produces a larger flame signature that usual which the company says will up the fun factor at the shooting range. The Citadel is currently available for 1/2x28 TPI or 5/8x24 TPI threaded muzzles for an MSRP of $109.99