The Japanese Tsuboman Atoma Stones are perfect to repair chipped knives, sharpen them, and even flattening whetsones, leaving a great finish. Diamonds are used to make abrasive tools, are the hardest material in the world, so they can handle any steel used to make knives, and even ceramic knives.
The biggest advantage of diamond stones is that they are straight and do not require flattening like whetsones.
The Atoma stone brand are made of a solid block of aluminum, and the diamond embankment is attached to a steel plate. Diamond stones will be a great complement to water stones - using them in the initial stages of sharpening will allow you to bring out a new edge of even a very neglected knife at a rapid pace.
The use of diamond stones is different from that of water stones. They require much less pressure, it is enough to use the weight of the knife itself when sharpening.