I haven't broken one yet since the only ones I use are the cheap plastic ones that come with my
tank. Any advantages with using a glass vs. plastic?
None in particular, except for what Ocelot pointed out about certain flavors being able to melt plastic or acrylic tips.
I prefer pyrex glass over any other material because of how it feels on my lips. It just feels better than metal, ceramic, or acrylic. Some people say that they can taste a metalic taste from using a metal drip tip; I can't, but I "feel" the difference of materials on my lips and tongue, and I know that I don't like metal.
Beauty is in the eye of the beholder, and in my eyes the glass tips done by the high end manufacturers are not only functional but beautiful works of art. Many are unique, one-of-a-kind creations. They are a fun thing to collect if you have the resources.

