Sadly, you invoked one of this forum's evil spirits, otherwise this could have been an interesting topic.
I'll be the unpopular one, however, and say that in the hypothetical situation that I was stropping to 1/10th of a micron for some reason and only had those two choices, I would go for the CBN. There are five different main factors that separate the compounds used in stropping:
1. Abrasive concentration
2. Abrasive scale consistency
3. Abrasive hardness
4. Abrasive shape
5. Carrier type (Water vs. oil, suspension vs. emulsion, etc.)
All effect the sharpening process. Ken's getting his gear from a known industrial supplier, possibly to his own specs for grit concentration and maybe consistency, and rebranding them/marking them up for retail sale. The compounds are decent quality, if expensive for what they are. If you do some research, you will find several industrial suppliers in the US making precision lapidary and polishing abrasives, and if you have the gumption you can buy compounds of similar quality to Ken's from them direct over the phone. It just depends upon who you want to give your money to, and if you want to learn more about abrasives and the companies that make them on your own.
According to the straight razor sharpeners who have dabbled in the dark arts, CBN particles tend to result in a slightly smoother edge at the .1-.125 micron level than polycrystaline or monocrystaline diamond, and CBN is also more suitable for power stropping with a belt grinder or buffing wheels. This is good for shaving, maybe chisels or carving tools (Never stropped one of mine that high), and imaginably is acceptable for certain types of kitchen or pocket knives for parlor tricks (Although diamond tends to retain its toothiness to higher grits.). However, for most food prep, this level of refinement isn't necessarily ideal (Especially if your bevel isn't perfect to start with.).
The suitability of compounds this fine depends upon your application, and how much you just want to experiment for the sake of it. I had a phase with strops, trying to see how far I can go. You can genuinely feel a noticeable increase in perceived 'sharpness' with each finer step, which feels cool for the first few cuts, but the problem comes when you use the knife for any period of time. Because the edge is so refined, there is no residual 'toothiness' to help keep the blade cutting into the food once corrosion or wear starts taking place, so it stops biting into the food very quickly. You can actually see this with a paper towel test... Roll up a paper towel, and try cutting into it. That highly refined stropped edge will only cut a short distance into the roll. A coarser edge - providing it is deburred - however, will saw deeper into the roll, and possibly all the way through. Throw some use into the equation, and that stropped edge will stop cutting into the paper towel long before the lower grit one. That coarser edge might not pass a shave test as well as a highly stropped edge, but will perform better on most types of food past the first few cuts, barring woody vegetables like carrots.
The really nice thing about pasted strops, though, is how easy they make it to obtain a 'clean' edge, free of burr. This is great when you first start sharpening, and sometimes even after if you're in a hurry. However, as weird as this sounds, you might actually find it more beneficial - rather than go finer than 0.5 micron - to actually go coarser than 0.5 micron if your application is food related, and try a diamond or CBN paste between 1-3 microns. You'll still get the clean edge easily, but will find more toothiness, and since the coarser grits will cut faster (Providing the concentration is decent) you'll actually be able to use it for touch-ups when the edge starts to wear rather than having to hit your stones again... You won't get as much of that initial light-saber feeling, but in the long-run you might grow into this toothier type of edge. Most people do.
However, if you just want to play, have a bash at 0.1 micron... The only reason why the cheaper diamond paste might be inferior to Ken's CBN is (A) - cutting speed, and (B) - grit consistency (Which means that the edge will never be a uniform 0.1 micron finish; there will be deeper, random scratches. Maybe not terrible for a kitchen knife, but unacceptable for a razor.). Because of this, the cheaper paste might not feel as fine or effective as the higher quality product, but whether or not this matters is up to you. If you want to truly experience 0.1 micron, I would also buy some 0.25 micron to fill the gap between this and your 0.5; fine strops are not fast cutters (Particularly at low abrasive concentrations), and need a tighter progression to fully erase the scratch pattern from the previous grit.
If the cheaper compound is oil based, it might also not be as easy to clean off the blade as a water-based compound. This isn't important for woodworking tools or pocket knives, but is important on kitchen knives or razors which are in contact with your food or skin.
Hopefully this helps...
- Steampunk
