SLP LoudMouths are basically straight pipes with tips (muffler delete) while the
Pypes Violators have louvered perforations in a tube that is encased in a muffler shell.
I've heard comparisons saying the Violators are one of the loudest mufflers available. I can't attest to this because I still have the stock cats, stock H-pipe, etc... but the Violators sound AWESOME. There is some drone at the 1500-1800 RPM range and if you let off the throttle on the highway to decelerate into this RPM range, you will hear the sweetest exhaust gurgle...
I'm satisfied with my Violators except for the way they engineered the hangers and the way they cut the slots in the connectors. I had to bend the hangers (using a MAP torch to heat them up and then bend them) and re-cut the slots so the muffler would "grip" the mid-pipes better. Otherwise they tend to get loose.
T-304 SS is more attractive than T-409 SS due to better surface corrosion resistance. However, T-304 SS is very soft steel... a die grinder on a low setting will cut through T-304 like a hot knife through butter. T-409 SS can be a b*tch and a half to work with, especially with the high grade T-409 with titanium in the alloy content. T-409 is chosen by almost all OEMs for its durability. It does develop surface corrosion but it won't rust through for decades.
If I had to do it again, I'd go with the less expensive T-409
Pypes Violators.