Pros : I too believe this to be one of the best tools for drilling clockwork holes in fused glass projects. Generally it doesn't slide around and makes pretty efficient work of the scary task of drilling through glass.
Cons : I don't know that I got quite the advertised 50-60 drills, but I am sure there is a lot of room for variability. As the bit wore I had some issues with glass chipping and did completely ruin one nice project.
Other Thoughts : I usually make a smaller pilot hole first and that allows the larger bit to stay positioned.