George;
That black one is used on a open flame, Korean meat is cut very thin and dries out and burns easily, So this keeps it above the flame. It is the same Idea as the BBQ pit in the Korean BBQ house. you can cook your onions, shrimp,scalops, everything on it.
It is mostly used on small charcoal grills Asian style ones that is another reason for the raised area. They do work rather well.