It allegedly works great. It empirically costs way too much except in unusual circumstances. For what some of my customers have been quoted for the Aeroseal service they could have just as easily bought an entirely new duct system. I don't blame the contractor directly. Rumor has it that Aeroseal charges a ton up front AND takes a percentage of each and every job.
our company offers this service, I personally have done it 6-10 times. some older houses it is amazing at how it works, we seal duct work to atleast 80% sealed. i see it more benificial on older houses. weved sealed houses that have been built in the last few years and duct work was pretty good be like i said sealed to 80%. worth the money oh ya,, i dont know what other companys charge but its a lot cheaper getting ducts sealed in illinios then getting a duct replacement.