No experience with a SG20k, but I can tell you, Shobu stones can be really good. The ones I've had the pleasure to try are very hard, and possess very strong cutting power on slurry (for finishing stones). It means they can give you a range of edges, from very mellow and forgiving as you say, to very sharp and harsh (for my skin at least).

I will agree, jnats are easier to work with than coticules, although I use a few lately... got one vintage La Petite Blanche that will likely stay with me permanently. Owned and sold a La Dressante, Las Petas, La Verte.. tried a La Grise a few times, didn't care for it at all. I also use a La Veinette, but mostly for mid range work when I feel like it. I can't seem to consistently make the transition from slurry to water, so that I get rid of all the deep scratches. This is a non-issue on my jnats, no matter the mine they came from.

That is a very nice Ozuku by the way, it will likely outlive us all!