I have the same air cut off tool, but it doesn't seem to work very well? You've been able happy with it?
I don't have Harbor Freight brand but have a good Ingersoll-Rand that I've been using for 25+ years now. They do use a lot of air volume and 3/8 line would be the minimum to use plus daily oiling before use is a must. Just a few drops of oil is all that is needed.
Dremel tools are fine for small work but any cutout hole larger than 2"x2" is going to eat up the wheels rather quickly on a Dremel.
1984 CJ-7 Renegade