No problem with the belt's wearing out very fast. Many more than three or four blades. I buy the belts in bulk and I think they are around $2.50 apiece.
As to the hollow ground edge. If I wanted to hollow grind the blade I could, utilizing one of the small bearings on the triangle of the path of the belt.
I quess I mis-spoke when I said "I've used them all". I haven't tried the Walls. My apologies!