Looking at patent drawings for some low backpressure (or flow through, as Hux/OSS trademarked) silencers in which blast chamber bleed off can bypass the main baffles, they might be more susceptible to unintended consequences of changing muzzle devices because a brake may increase the amount of “gas” that bypasses the main baffle stack. Or, inversely, a flash hider might decrease the bypass. This is probably why Hux’s “flash hider” is actually a brake designed to look like a flash hider design from the side. You’ll notice that their website avoids showing it from the front. This isn’t to knock Hux; obviously they feel that their design is better when paired as intended. The reverse-compatibility concerns their engineers have to deal with are different from the reverse-compatibility concerns that Surefire, Geissele, or Silencerco engineers have to deal with.
For traditional cans, a brake might reduce the amount of gas that can flow straight down a short and oversized bore without interacting with the baffles as much. Like my Rex .458 K can on a 5.56 gun, for example.
@Green0, that 20% formula…do you think that applies to sound as well, or would you apply a significantly different factor to your expectations in that area? 20% of an AEM5’s reflex chamber length would be like .4”. If reflex chambers are that inefficient at sound reduction, that would explain why they’re not more popular.