On the GradeMaster units, the way I understand it, some of the dirt will flow over the top of the blade and some of it will flow to side. The dirt that flows over the top of the first blade may very well flow to the side of the second when it then may flow over the top. Like I said, I've actually never seen one work but I had heard about them. I would love for someone with actual experience to post some information about them and how well they work and why in some instances they may be better than a box blade and in other instances they may be inappropriate.