Hi Assaf
I do not see an advantage with a rounded bevel. The rounded bevel is simply a product of the sharpening method. More importantly, the leading edge of the secondary bevel is 35 degrees.
This method is easier, in my opinion, when freehanding a secondary bevel on a mortice chisel with a deep blade and a 20 degree primary bevel. My Japanese mortice chisels have shallower blades and there is no secondary bevel, just the polished primary bevel. Note that I am freehand sharpening. If I used a honing guide, it would make sense to add a secondary bevel.
Regards from Perth
Derek