So yeah, I think they are extremely durable but you can ask just about anyone who owns them 
But no matter how the quality is, these tips are still made of glass so breakage is possible. I have a little girl who is about to turn 1 and walks, she really likes grabbing me and my wife's PV's... She has dropped, thrown, and knocked them over each week for months but hasn't broken one yet. (I should also note the Mrs only uses glass tips as well, though she has only 3 while I have a small collection)
OH! Almost forgot, if you want to try a glass tip out, without the risk of a 25 dollar investment, just get some Buddy Tips
They are free and you can choose your length
But no matter how the quality is, these tips are still made of glass so breakage is possible. I have a little girl who is about to turn 1 and walks, she really likes grabbing me and my wife's PV's... She has dropped, thrown, and knocked them over each week for months but hasn't broken one yet. (I should also note the Mrs only uses glass tips as well, though she has only 3 while I have a small collection)
OH! Almost forgot, if you want to try a glass tip out, without the risk of a 25 dollar investment, just get some Buddy Tips