Generally diamond sharpeners work well, but...
When diamond hones are new they are coated with diamond grit that is pretty uniform in size, but it is not neat little spheres or cubes. It is a variety of oblong crystals laying at a variety of angles. This leads to an uneven surface. This grit is sharper than most other abrasive grit and harder. Initially a diamond hone cuts very fast, but rougher than you would expect for its grit size. The diamond grit is so hard that it takes time for the tallest grit to break off and the hone surface to become more uniform. It starts cutting slower and smoother at this point (some people think that the hone is wearing out at this point, but in reality it is just getting broken in). At this point the diamond hone cuts faster than most other hones and just about as smooth. The slight surface texture left by the clean-cutting diamond grit can even be an advantage for slicing.
The coarse diamond hones are for reshaping a knife edge more than for sharpening. If you have a knife with an obtuse primary grind you might want to reprofile it using a coarse diamond hone. I usually use a water stone or a belt sander for this purpose. They both leave a cleaner finish than a coarse diamond hone. What I really like are the fine and ultra-fine diamond hones. These cut faster than other hones in this grit range. They also tend to clean up burrs left on the edge. I am talking about broken-in hones in this case. An ultra fine diamond hone leaves a very effective edge on a knife. It will also do a good job on extremely hard or otherwise uncooperative stainless steel.