If you're afraid of it breaking, think of the products you already own that are made of thick, high-quality glass. How often do those break? Is it likely enough for you to worry about? Probably not!
I made the decision to try glass when I remembered that I've worn glasses for probably ten years now and all manner of things to them have happened over the years, and yet the most broken any pair has gotten is the screws falling out. Why would I expect something that was specifically made to be in my vagina to be weaker in my vagina?