You could actually remove the factory muffler and ride the R3 like that--I did. The catalytic converter is the back pressure regulator, not the tractor muffler Yamaha stuck on the bike. The one ride I did without the muffler made the bike sound like crap, so my new slip-on from Devil Evolution is on the way. I looked at the Coffman muffler as well, but did not like the black finish. I did like the fact that you do not need to connect a bracket, but you do need to drill for rivets to keep it from rotating around the pipe.
I also liked the included filler piece for the opening left in the body panel from getting rid of the factory muffler. In the end, though, I liked the polished finish and design of the Devil Evo muffler, and it's "high exit", which is even cooler. Google search "devil evolution D5M slip-on muffler for Yamaha R3"