The glass they use is the same as Pyrex. They're not indestructible, but with regular use, they would be okay.
DH is a material scientist, I asked him a while ago what he thought about using them. He said there wouldn't be a problem as long as you weren't hard on them. He also said they were pretty expensive in regard to what it probably costs them to manufacture, but then again things are worth what others are willing to pay.
He promised to make me some, but the excitement of that promise has worn off with age. :rollseyes: