I own the Sharpmaker with the diamond and ultra fine stones as well as several other benchstonesbenchstones.
The diamond will help you reprofile to the proper angle on the Sharpmaker, I would highly recommend it. The ultra fine not so much, I would consider it an accessory to get after you get the diamond if you felt like it.
When you sharpen a knife the goal is to a fully apexed edge free of defects. That will make a sharp knife. If you finish on a coarse grit it will create a more toothy edge which excels at slicing. If you finish on a finer grit you get a more polished edge which excels at push cutting. They are both equally sharp.
A lot of people are under the misconception a higher grit stone will make it sharper. The reason is quite simple, it wasn't properly sharpened when they finished on the coarser stone so the extra time on the finer grits is helping them. They also may be trying to do things like push cut paper instead of slicing which prefers a more polished edge. If you try to tree top hair, once again a more polished edge is more effective than a toothy. In real world use it doesn't matter what you finish it on as much as your trying to cut material, not do party tricks to show off it's sharpness.
