Pros : I rated this a year or two ago and gave it five stars. Now for some reason it has really deteriorated. I can no longer provide pro comments. See description of cons below.
Cons : I teach classes at a community center. Generally a class runs seven weeks, three hours per week with a max of seven students. Three Superstar grinders are available for student use.
The last two classes, I have needed to use six or nine bits, where in previous classes, one grinder bit per grinder was adequate.
The bit has less grinder teeth (or whatever) and grinds down to flat metal very fast. I watch the water levels, and regularly adjust the bit up and down.
I plan to discuss this matter with Delphi (they now produce the bit, I think.)