FWIW: I am running a Bisson Pitts muffler on my SuperTigre G-75 and it purrs like a kitten. Note that the ST carb does need careful adjustment on the low-end needle. I had to spend some time (and get some help from a more-experienced engine guy) to get it just right on idle. No problems with back pressure or fuel flow.

As others have said, the Bisson mufflers are a bit larger than the Slimlines and probably a bit quieter. Go with what fits, I guess.