Without checking out a sample of the product itself it's difficult to say exactly how good the material is but broadly speaking this kind of elastomer dampening sheet works more-or-less the same regardless of who makes it.
$2 per sq foot is not expensive, compared to other similar products.
You have to realize this will not take the place of rockwool/fibreglass/wool fibre damping which is there for a different purpose. This is really only going to do the same job it would on car panels and sheet metal: dampen resonance of the cabinet itself.
There are many ways to improve cabinet resonance behaviour so this is not the only possible solution by any means. If you have a well braced cabinet made of appropriate material and density, it might be worth looking at to take it to the next level. Having said that, good basic construction works well and this product isn't going to turn a flimsy box into concrete, or compensate for a weak mounting method, or clean up rattles and vibration that originate somewhere else in the car.
As always, adding something to the interior of a speaker cabinet (besides materials that hold dead air) will reduce interior volume. This may have an influence on overall response, especially if the box is already too small to be optimum, or if you did not compensate for the displaced volume of the speaker and crossover, etc when you designed the cabinet for the driver.
The BBC did research which concluded 12mm marine-grade plywood damped with bitumen pads provided the most neutral cabinet. This is 1970's stuff, and few modern loudspeaker builders would choose such a thin plywood for the cabinet these days. "Normal" plywood is unsuitable, but marine grade has zero voids, many more laminations per inch, and uses waterproof glues. The waterproof glue is irrelevant, but the other two factors make it much more expensive than standard plywood, and also makes it suitable for high strength speaker cabinets where mdf is not durable enough.
Bitumen is commonly used in the kinds of damping materials you're looking at.
The BBC study does show that there might be a beneficial damping effect with this material in loudspeaker enclosures. The question is whether a properly designed cabinet made of conventional 5/8 or 3/4" material can benefit, or only a more resonant one of thinner material will.
Finally, if it's bass cabinets we're talking about, there is the question of whether there is any need for a "neutral" cabinet at all, rather than one that simply doesn't rattle too much. For car audio we normally don't put the mid and high frequency drivers in cabinets, where neutrality would be most beneficial.
