David Weaver
the edge looks more uniform, which is all the middle stone is really designed to do.

They often catch fire in peoples' reviews for not being fast enough or fine enough, and what we know of sharpening (the roll or the microbevel), they aren't absolutely necessary unless there's a flat bevel or relatively large facet involved.

I don't know what the s-t 4000 is, but I'd guess it's around 5 or so microns, the shapton pro is something like 15 or 20 (and this is probably starting to sound familiar with a diamond progression if you use a middle grit).

visuals are difficult before a polish is achieved other than to look at the line left at the edge and the depth of the divots (and make a mental correction for unevenness that's just wire edge).