I'm 99.9% sure it's not. The 3M stuff is more a rubbery bedliner type stuff. Spectrum is hard to describe, more a soft plastic than anything. They are also completely different colors (yeah, I know, that's not exactly a big deal).
You're probably right. But my point is there is a producer out there somewhere and buying direct might be cheaper. I also think that if you are using the same butyl product (whether it is called Damplifier, Roofing stuff, or butyl adhesive), with the same adhesion, in the same amount, the result will likely be the same.
But I do have doubts that you can easily find a significantly cheaper alternative when you factor in the cost and convenience of a ready to use product. The other thing to consider is the adhesion of the product. Damplifier, like butyl adhesives, sticks to the metal by itself. I wonder if roofing materials use the stickiness of the butyl or if they use some adhesive since roofing materials may have to stick to other materials (wood). That adhesive my detract from the effectiveness of the product 9or maybe not).