Round V-blocks - video

Round V-blocks. By The Machine Shed. 7:01 video:

https://www.youtube.com/watch?v=ur4toH_eLT4

Is there a advantage to using round vs regular V blocks?

Hi Ralph: The only advantage I see is it will support larger diameters before reaching the edge. While these are for clamping while milling and not precision grinding they may not need to be matched pairs. One dis-advantage is how to make the set accurately. Precision grind the OD and then mill and grind the steps for the T-slots?? I have also see a "V" block made from 4 ball bearings in a ring with the part resting on the curves. 4 point contact compared to a V block with 2 line contact.
Carl.