I'm from Belgium, a country that is absolutely hostile to aviation an other hard disciplines so model airplane pilots have a hard time to survive here, for all kinds of reasons. Let's say we are tolerated for the time being. Pitts style mufflers are absolutely not alowed over here , so when we order a modell, a canister tunnel must be provided which is in many cases a problem because many manufacturs don't take account of that.
A canister complicates the engine plant considerately, as I said you need space to put it and it must be properly mounted or you have
nothing but trouble with it even when you don't care about rpm loss. I have had some trouble with failing headers as long as I use them and they are quite costly. If you don't need them and you are already deaf or you don't care becoming it, don't use them I would say.