i dont think they work as well b/c they arent as thick...i believe they are for like hard to reach areas and what not...maybe even under the chassis of the car for odd places.
I did my entire car interior with eDead V3.. I was fairly happy, but it dosnt help much as far as rattles, etc. Honestly, I'm much happier with the new non-liquid stuff I'm slowly getting put in..
yes they do work.. liquid dampeners are mainly to add wieght and will benifit more when used over an existing matt like dynamat or damplifier.. secondskin has 2 products.. a thinner one that can be sprayed - spectrum and a thicker one (really thick) that can be troweled on called sludge.. when used by itself they will do more to eliminate rattles and vibrations than eliminate sound, course if you eliminate those thats sound too.. they can be sprayed/troweled whatever on top of an existing layer to make them more effective.. closed and open cell foams will kill alot of sound by absorbing/reflecting it before it gets into the vehicle