You really need to be talking apples to apples here. Brown Bread was made by B-Quiet, and is no longer available, and hasn't been for years. It has been replaced by B-Quiet Ultimate which has a higher butyl content. That means Brown Bread was part butyl and part asphalt, as is Ultimate.
Dynamat Extreme is totally butyl based, which means it is rubber, and has no asphalt. The other types of this product that are not butyl based are asphalt based, which means you might as well use roofing products.
Butyl based products are going to be more expensive than asphalt based products, and are going to be more heat resistant than asphalt based products or any combination of butyl and asphalt.
Closed cell and open cell has nothing to do with sound deadening or insulation, it refers to foam, like polyurethane, neoprene, and any other types of foamed products like PVC.
While any foam will demonstrate some tendencies to have sound deadening or insulating properties, it would not be superior to 100% butyl based products.
BTW, Shawn..........thanks for opening up this can of worms. There are Republicans , Democrats, and Independents, all of whom will tell you their ideas are superior. This topic has butyl proponents, butyl-asphalt proponents, and asphalt proponents, all of whom will tell you that their products are superior.
The other proponents are those of the Lizard Skin type products and people who will tell you that Lizard Skin can be made at home for a fraction of the cost.
Check out this thread: alternative to Lizard Skin
Let's see if you can read this thread all the way through.