I just noticed an Arkansas stone in the BST, And that got me thinking.
I've been using "soft arkansas" stone for years as the final stage in sharpening my pocket knives, and I know these are readily available at a fairly reasonable price in a decent sized brick for honing. Would one of these be a reasonable substitute for a "coticule" or similar fine stone if properly lapped?

I currently have a 4/8 norton, and Cro strop, would this fit in between, or be redundant?