Pros : I find this useful if I've fired some glass and I then want to reshape it a bit. On unfired 3mm glass it is fast and easy to use. It definitely saves you time. I will definitely buy this again.
Cons : The coarse grit is only to get a quick fix. It does chip your glass slightly, which is expected. I always make sure I then use finer grit grinding bits to ensure my pieces are not chipped.