Natural stones are what they are : natural, random, a bit chaotic.
I have hear as much discontent on the JNATs as I have on the cotis.

Granted, the first coticule I bought is a truly wonderful stone. I have learnt a lot thanks to it.
Luckily, I was offered one with a set of razors on a flea market and it was nothing alike : a grit lower than my BBW and it's damn aggressive.

The thing is, if you want natural stones, that you must build your progressions for what they really are and not what you hope they are. They don't have a calibrated grit, and hell, you don't even know what it is even about beforehand.

So, what to think of this very agressive and rough coticule ? Not the "pivotal universal stone" that the coti is sold to be, but looking at it the other way, it's a damn good bevel setter, and I can say that my progression is coti 1/bbw/coti 2 (the BBW/coti 2 is a combo) and I find it damn fun.

I've read "gentleman stone", I would likely more compare it to manual/automatic driving.
Manual requires a bit more skill, is rarely as efficient as automatic (when it comes to the mechanic of it), but you can push your skills to the finer grains and have more contrôle.
Cotis and every stone which produces a slurry anyway, are "manual" : no calibrated grit, but the ability, with the slurry and the correct feeling to "fine tune" everytime.

My advice : start synthetic, build a calibrated progression, buy some natural stones, try them and put them where you feel they work the best in your progression.

(little trick : you want to push a finisher "a bit further" ? Try a drop of liquid soap)