I used to do it one at a time too. I used a tapered DMT rod, which allowed me to fit whatever scallop size I was grinding perfectly. This method produces a prettier result, but over time, the humps between the scallops stay thick even though the cutouts between are being ground thinner. You end up with more of a saw-er instead of slicer
Sal's way of grinding everything evenly avoids this problem, even though it looks a bit sloppy. Everything wears down at the same rate, so you keep the relative profile of the edge closer to factory performance.
All that being said, you want to it a specific way, and for that I would go DMT. No guesswork with the diameter because of the taper, and less of the burring annoyances of straight ceramic.