I do know this about all insulation both bat & blown, it compresses & disappears into thin air over time and that is with no disturbance or other force applied.
Back in the day I was a biker & during my time in Colorado I would go down to Denver to party, heading back up to Summit County could be a very cold ride. I learned a trick from a bro of putting a newspaper inside my jacket which actually worked rather well. I was still frozen solid when I got home but alive ... ahh youth. It was also used for insulating homes prior to fiberglass. Not saying you should use newspaper but you get the point.
The older I get the better I used to be. Superhero status is near.
The reason fiberglass insulation is 'itchy and irritating' is because of the binders used on it. The binders (glue) keep everything together in the bat. The newer blown fiberglass (both pink and white) do not use binders at all (to help keep loft by reducing weight and thus settling in the attic). If you have this type of insulation left over I bet it will work and not be itchy; I would not try it with any insulation that has glue in it (bats).
However, the other properties will likely make it poor for our purposes; namely compression and rebound. I don't think once compressed it will fully loft again;or not very easily anyway. Weight would proly be the other reason; I don't have a specific weight per volume for blown glass insulation, but I will look tomorrow when I get to work.
Don't forget the obvious - IT'S MADE OF GLASS! Get a little in your eye and you'll know it for a long time, maybe forever. Same if you get it in your airway or lungs. It can be very dangerous and it is hard to contain when what it is in is fabric that is being moved and compressed. It is made to be installed and left alone. It would be interesting to see how it worked in a quilt but the risks are not worth it to me.
Johns Manville (the white stuff) specs for Climate Pro are this:
0.155 pounds per square foot
Effectively it is 2.48 ounces per 691.12 square inches. So, for 900 square inches it would be 3.22 ounces or a fill power of 278.67 square inches per ounce; roughly 1/3 that of 900 fill power down.