Seal and Peel eh? Good luck with the smell and I hope it lasts longer than 6 months. The bigger issue isn't cost it's quality. First, weight is your best friend when dampening. Second, you MUST achieve that in the first layer because adding over top the first significantly detracts from the qualities that provide the dampening. The return on that idea is almost voided.
Next, dampening and sound deadening are two distinct issues. You can have one without the other however you don't achieve both in a single product. Honestly, even duct seal works depending on the application and goals. But don't confuse products with applications and goals. They all have their purpose. If you live in a somewhat mild climate then peel and seal could work well.
