Everyone in my shop uses 4"x10" DMT diamond plates to flatten the backs of chisels, slicks, and plane irons. We work with Japanese tools exclusively and only flatten the area directly behind the cutting edge, which is extemely hard, so I dont know how they would work with western tools in that application. A two sided plate with black(extra course) for flattening our waterstones and blue(course) for flattening blades and removing small nicks almost negates the need for power tools. When we get huge chips then we might use a grinder with a ruby wheel to put a hollow grind on a blade which makes for quicker material removal.