RRob, I think a hollow grind is used so that it's quicker to flat sharpen two narrow strips on either side of the hollow instead of the entire bevel. What ever method, it might not be a bad idea to put a tiny secondary bevel on a sharpened edge.
I personally don't like a guide that rides on the sharpening surface, though it's a preferred system. I think it's easier to ride off the surface and harder to keep the sharpening surface flat if it's a stone. That GW is a fancy and pricey guide, so it probably doesn't matter, but if someone uses sharpening stones, as the size goes up a little, the price goes up exponentially. Only thoughts.
