No crush washers and you can easily retune for different ammo on the fly! a great product! - ODIN Works ATLAS Compensator

These are so good there are cheap Chinese knockoffs for sale on fleabay, but do NOT buy a knockoff. Get the real deal. The fact you can adjust this means you don't need crush washers which will destroy your accuracy. You don't need shims, but I'd use a shim anyway. When you ram a brake or flash hider down onto a crush washer you pre-torque the whole barrel and you also torsion tweak the muzzle too. As the barrel heats up your zero will go bye bye. When it cools down it won't be the same again either. This device helps avoid all that. The recoil reduction is north of 50% and the muzzle climb, flip and twist are mitigated nicely.