The first step toward getting these to breath is to grind the awful OE Honda exhaust flange welds. Honda welds up the pipe to the flanges unbelievably sloppy, so that the pipe is restricted 20% or more of its diameter. Take a look:
That is not carbon buildup, it is the weld itself. Some time with the Dremel and you can see the difference on the left side of the flange.
Added an FMF Q4:
Workmanship is great and the bike sounds good and is not loud.