Arks, jaspers and spydercos make decent very hard platforms for nagura honing.

I've tried this before with one of those phigs with stretch marks on it (you know, the good ones) and ultimately contaminated my stone at the end with chrome ox powder (something that was easily rectified later).

Anyway, I don't like the spyderco as a base (even the 8x3 UF after it's been used on tools to the point that it's not cutting anything), and not necessarily the jasper. In my opinion, if a stone has good feel and will leave a bright polish on clear water, I'm OK with it. If it doesn't have a good feel, then I'll find a stone that has a good feel.

Jaspers and settled in spydercos are more like burnishing plates than anything else, and I can't remember what I concluded with the arks, but I don't like arks on clear water to begin with , I like them with oil.

So, my vote is that a good phig is a decent basis for nagura use, but a dud phig is still a dud phig, and none of my phigs have been the same (out of four). The one with the stretch mark looking things was fantastic, two of the others are marginal and one was soft and released grit and was really unsuitable for anything.

Oh yeah, of course the plate has to be a non-scratchy stone.

Some of the shoubu and ozuku stones are so inexpensive now, even in hard state, that it's a better bet just to get a razor graded hard stone from a reputable dealer than it is to waste $150 on big phigs hoping you'll get one good one out of four.