Flash suppressors typically aren't the problem, they don't redirect muzzle blast to any real extent, they just break up the flash signature.
Brakes (compensators) on the other hand, function by redirecting the muzzle blast. Generally, the more efficient they are at taming recoil and muzzle rise, the more obnoxious they are to anyone seated to either side.
I don't like the brakes and I feel that people that use them should exercise some common courtesy when it comes to their fellow shooters at the range.
This gets me a lot of "F_ you! I will do whatever I want and if you don't like it, LEAVE!" comments from other shooters.
Brakes are not made for close-quarters seating. But they do serve a purpose and there's nothing inherently wrong with them as long as the owner mans up and treats his fellow shooters with respect.
Sadly, there's way to little of that behaviour anymore