Excellent stuff. I have had great results with their high-end products, both the B-quiet ultimate as well as the L-comp. The ultimate is quite durable, very sticky [doesn't fall off] and has good attenuation characteristics. The L-comp is a lead-based product...oops...just checked the site. They aren't selling it due to the high cost of lead...
Anyway, I have had superb results by using a 5 gal bucket of Quiet Car goop, 50 sq ft of B-quiet ultimate, and 8 sq ft of the lead product. Lots of added weight but awesome results.