Taidea T0905D diamond sharpener is a small, pen-sized diamond sharpener that comes with 2 sharpening rods. One rod is half flat, half-round with a groove running down the middle of the round side. The flat side can be used for sharpening plain edge blades. The groove is useful when sharpening fishing hooks and similar, small, pointed things. The second, tapered round rod, is good for sharpening serrated knives and other serrated blades. The taper allows you to sharpen different sized round serrations, including the annoying ones on a bread knife. Sharpening serrated knives isn't that hard when you have the correct tool for it.
A diamond sharpener suitable for many kinds of sharpening needs and will sharpen all kinds of steel.