Looking at the specifications on the page you linked to, it appears to be made of the same basic materials as other duct tapes: plastic coated fabric with a rubber adhesive. Premium Grade it may be, but I think you'll run into the same problems -- it'll get brittle and crack with age. I've used aluminum foil tape where I've needed spot repairs; Home Improvement 1-2-3 says to use duct mastic when installing ducts.
I found this article very useful: Can Duct-Tape Take The Heat?
Duct Tape Cannot Take The Heat
Although our testing has not been able
to differentiate amongst other sealant
products, the data shows that cloth
duct tape is not a good sealant for
use in ducts that operate at much
above ambient temperature. We believe
this is due to the rubber adhesive,
but cannot state so definitively. For
the most part, cloth backing and
rubber adhesives go hand in hand. Thus
it is not surprising that the other
sealant products have not demonstrated
any of the failure modes we have seen
in the duct tapes. There are a few
products that use rubber adhesives
with non-cloth backing and we intend
to test these in the future.
To address your side note about Class 1 ducts: from the scope for UL 181 Standard for Factory-Made Air Ducts and Air Connectors
Class 0 - Air ducts and air connectors having surface burning characteristics of zero.
Class 1 - Air ducts and air connectors having a flame-spread index of not over 25 without evidence of continued progressive combustion and a smoke-developed index of not over 50.