Mark, I have never heard of asbestos being used in fiberboard duct.
I think the fiberboard is a pain in the butt from a homeowners point of view. It sure is easy enough to install though. I remember replacing a few pieces when we installed new AC units and had to make up a new transition pieces. A couple simple tools and special cutters for making rabbits and miters, a razor knife, and a few rolls to metalized tape and you are in business
But for myself I would not want it in my house. The air breaks off small pieces of fiber that then float out the duct and into the air you breathe and it settles out on everything making a dusty mess. Can't be too good for your lungs either.
