There is the peel and stick Butyl with the aluminum face for roofs, and there is peel and stick Butyl with a white face for the perimeter of residential windows. I'll assume the aluminum faced can handle higher temps, and the white facewd stuff does seem to be a bit softer, and stretchier.
I will use either, but I cover the exposed edges with Nashua Flexfix 555 Tape. This is not the regular aluminum tape, this stuff is flexible and does not tear as easily. It's been on the inside of my engine cover closest to exhaust manifolds for 14 years. No durability issues.
I recommend wiping the surface with Isopropyl alcohol before bonding either the peal and seal or the flexfix tape.
I too have no basis for comparison to a $$$ product like Dynamat. The peal and seal stops large sections of flat panels from ringing like a bell when struck with a knuckle, but sometimes a few different size patches have to be stacked to stop it ringing.
Sound deadening can be taken to extremes.
If Ram4Ever reads this, well he has gone there and redefined 'extremes'
I just use a knuckle, and any improvement is appreciated.