guys, my mivec is set up with 2 inch piping with aftermarket local made 421 , 2 inch mid bullet and 1.75 inch Hotbit Super turbo muffler ( N flow ).
There is no disadvantages to use on s flow muffler. The most important is the muffler diameter size. overall, 421 and piping diameter are playing most important part in exhuast system.
S- flow muffler even though can work like N group muffler , u just need to prefer on bigger diameter muffler set up .
U guys can prefer to NZ mivec club posting, almost stock condition mivec can clock with 14 sec flat in 400m drag ... and the muffler set up is using s -flow muffler.
And I very strongly recommanded on Hotbit muffler, light weight + reasonable price and power u can get.