yes it is made for bending it on archways.
I have not come across this stuff yet, as I have only used straight stuff.
I would say, use straight stuff where you can. They should take back unused lengths of the ones you have. And, where you have to,
just dump mud on it, and let it dry one to two days, then sand by hand for a perfect finish. I don't imagine the radius should be muded too much, it should be feathered up to it, but not on the radius it's self.
Let it dry hard hard, then sand for a perfect finish.
Please post pictures when available,
good luck with this project.