Well they didnt bother to clean the ducts they repeatedly told you were dirty before they coated the system in glue.

1. Way more expensive than grabbing some duct sealer and going to town.
2. It does work if applied properly and there's no large flaws in your system.
3. It will generally make your system more effective if done properly

My advice is to get a roll of tape and some sealer and take care of your attic and any exposed areas. Then spend your money on extra insulation, assuming you aren't selling in 5 years or less.

Any leaks inside an interior wall cavity will simply move the btus in a less direct fashion.

That hepa extraction filter thing doesn't get it all and your place will be coated in a thin layer of glue. You pretty much have to cover everything you dont want to scrub.

If your home was built after about 2000 with an energy star rating it was supposed to have sealed ducts to begin with