I was to understand that the Nagura needs to be from the same or harder stone to produce an efficient slurry. I was surprised when I was given a different stone as a Nagura which produces a slurry from itself rather than from the actual hone and changes the whole effect of things, so I don't use a slurry.

I think that could be half the problems others have encountered, using an inappropriate Nagura for the inappropriate hone.

That is just my opinion and as usual YMMV.