I just bought a set and was on sale $12+shipping. Installed yesterday & I have to say there is no noticeable difference in sound level at all. I measured with a sound meter before and after & it says it's a few decibels quieter. I guess that's something, but my naked (albeit damaged from years living aboard a ship only meters from the massive diesel engines) hearing. They are substantial and the adhesive works well, but they do not noticeably reduce engine or gear noise as advertised. This is in NO WAY a criticism of JNM or their products or services. I've bought many items from them in the past and was pleased, and in this case, like I've said, substantial, well made, good adhesive. Easy to install. In my experience only, no noise reduction. Could simply be my crappy hearing.
Anybody else buy these, have any feedback? I'm curious to know if others had had different experiences. SBP sells them too.