I know at least one person who has used them but apart from that it seems that they aren't very popular
ok here are some examples, I esspecially like the coaxial ones
(circular patern inside a pipe shaped extrusion = instant coaxial


this one would make an awesome readymade silencer

I am well aware that it might not be strong enough for high pressure pneumatics or high mix hybrids
(one could always use inserts made from steel)
Anyway I want to know what's you opinion on this What do you guys think?