As always, you have to define what you are trying to accomplish. Claims of a fraction of a decibel increase, despite being just as likely cause by a change in temperature or barometric pressure or a dozen other unrelated factors, if true are proof that these materials don't work as a vibration damper. An effective vibration damper will decrease pure SPL because some sound energy will be converted to heat. If you are only interested in numbers on a meter there are better ways to brace a panel - although relatively stiff asphalt materials might help a little bit for those who are willing to risk product failure and aren't willing to do the harder work that will return larger gains.
Similarly, claims about reducing rattles don't really tell us anything about the effectiveness of a vibration damper. If two adjacent parts are making intermittent contact when vibrating, duct tape will work just as well.
Use a vibration damper when you are concerned about noise - to prevent sound transmission through the vehicle's structure and to prevent the distortion to your music that occurs when vehicle panels resonate and reinforce the sound at those panel's resonant frequencies. If you need a vibration damper for either of these reasons, or if you care about the long term stability of the things you put in your car, asphalt isn't a good choice. Asphalt is a terrible vibration damper and it has a very high failure rate in cars.