It's been proven that (on the Liberty at least) the BowTech silencers are within about 1db or less on average as far as noise reduction VS. the SIMS Leeches, so it's safe to say that they do work well.
String position as well as individual set-up will determine how much abuse they can take.......my Liberty at 30"/70# eats the bottom one up real quick down low because it snags the string near the cam.
The top one still looks new after a ton of shooting.......
I finally got tired of taking my string off to replace the BowTech ones and put some SIMS leeches in that I had lying around the other day and I cannot tell a difference in noise reduction.
The Leeches are just more convenient to use, that's all IMO.