Someone correct me if I am wrong....
IMHO, for the most part all they do is redirect the blast wave, away from the trigger puller. So for me , the sonic pressure created via the blast wave, is jetting forward with a linear comp.. but the noise is still there.
You are directing the muzzle blast into an expansion chamber, and giving it much larger cross-sectional area when it finally does expel into your arena. That will "lessen" the sonic pressure and blast wave very slightly... and blast it forward.
If it helps, that same blast wave is what makes brakes so effective... redirecting the blast off to the side... and the noise.
It will still be loud as heck indoors.
To me, the linear comp is more about the lessened side muzzle blast , not about being quieter.