Interesting that they are all round shank. I made one with a round shank and I seldom use it. Having a flat surface on the tool rest just seems to give me better control. The round shank has a tendency to twist sometimes.
OK, I should have looked at the description in more detail.
It looks as though there are 3 sides of a hexagon milled into the bottom. This would give a 30 degree angle on the cutter in both directions. Interesting concept.