When sharpening things free-handed, the ability to keep a fixed sharpening angle is everything. On knives squeezing the last bit of keenness out of the Coticule isn't as important as it is with razors. For kitchen knives, cutting vegetables on a wooden board will remove shaving sharpness withing the first few cuts. That doesn't mean that shaving arm hair isn't a very good test for checking the results after sharpening a knife, chisel or some other tool. But I wouldn't be bothering with hanging hair tests.
If you are in the habit of maintaining sharp edges on your knives/tools, as any professional cook/carpenter/butcher/etc does, a Coticule will work quite well for sharpening and touch-ups. But, in most households, knives are notoriously dull. Being a sucker for sharpness most of my grown-up life, I can't help myself to sneakingly check the edges of kitchen knives, whenever I see one of those nice blocks filled with expensive cutlery in the homes of my friends. Almost without exception, these knives are dull. Not butter knife dull, but still... If you throw a tomato to the edge of a knife and it bounces back...:-/ And the owners of these knives use them like that. My friends do that, my parents do it, even my wife does it. And I don't think they're exceptions. One may wonder what the point is of buying premium quality knives, that can take and hold excellent edges, if we'll be using them dull anyway. But I digress.
The bevels on such knives, that haven't touched a hone in a year or more, need preliminary work, before a Coticule can do any meaningful work. Certainly if the knives are of decent quality. In these cases it's best to restore a decent cutting bevel with aid of a coarser sharpening stone. Carborundum in the 300-ish grit range, or a diamond hone of similar coarseness is fine for that.
The most used sharpening approach is this:
Normally you just hone one side, with back and forth motions, following the curve of the blade, till a bur folds over at the opposite side. This can be easily felt with the fingernail: try plucking the expected bur as if it was a string, if it's there, you'll feel your nail skipping over it. Make sure the bur is present at the entire length of the blade.
At that point, turn over the knife and work on the other side till the first bur is gone and a new bur folds over at the other side. Again, make sure this condition is met at the entire edge.
Now the knife has a decent cutting bevel.
[note]If the knife was well maintained, this can be done with a Coticule. In that case, it's important to know that the bur created by a Coticule will be extremely small and harder to feel than the large bur left by man-made sharpening stones.[/note]
As said, the result totally depends on your ability to keep the honing angle constant. You need to focus on that real hard, and as Kinematic already pointed out: lock your wrist and do not allow the angle to vary. I usually put the knife at 90° on the hone, divide that in half (45°) and once again, to find 22.5°, which is close enough for me.
In case you used a coarser sharpening stone to restore a decent bevel, repeat the entire process on a Coticule (raise bur on one side, flip the knife and raise bur on the other side.)
Flip the knife one last time and end with just enough "edge leading"-strokes to remove that last bur. It won't be more than 10-15 strokes, depending on the Coticule and its size.
Done. If your angle consistency is any good, you should be able to shave arm hair, but if not, the edge should still be good enough for decent kitchen-service. And by that, I mean that you can slice a tomato by throwing it at the edge.
As a rule, Coticule edges do not need to be steeled. Simply touch them up on the Coticule (water only), by making a few strokes on either side of the edge. Such maintenance strokes must be made frequently, at the first signs of performance loss.
Remember: keeping a constant honing angle requires experience. There are a few different tricks that can make it easier, but they don't replace practice.
You can fold a 22.5° angle with a sheet of paper, and use it as a visual aid to keep the correct angle.
Another possibility is to build a small angled support for the hone. This puts the Coticule at an angle and allows you to keep the knife horizontal, which is much easier for most people. But the downside is that slurry doesn't stay on the Coticule so easily.
Kind regards,
Bart.