I ran the SEI brake on my 18.5 inch barreled guns for about a year and a half....then I went hunting with one of my M1As and made the mistake of discharging it towards a mule deer down in the bottom of quite a tight draw. As I was wearing no hearing protection, it took some time for the ringing to go away! I've since switched them all out for Smith Enterprise Vortex flash hiders. If anyone is looking for an SEI brake, send me a PM as I have lots of them and would not mind selling off 3 or 4.
What's nice about them is they use the castle nut and barrel splines to attach to the barrel....this means there is no modification required to use with a factory norinco barrel. They also have a dovetail for a standard M1A type sight....no fancy gas lock required. They also appreciably reduce muzzle climb and felt recoil.
What's bad about them? Only the noise....
Cheers,
Brobee