i've used one and sharpened 2... rustic, yes... but nice overall. I find them a little on the tall side for me and the tip shape is kind of wierd to me, but it works just fine on those knives. Sharpening was a little more difficult than i expeected based on my othr experience with yellow steel, but still not too bad. I did get some chipping on the edge when i slammed it down on my board, but then again i slammed it down on my boardSome chat about Sadayasu here.
Jon, have you any experience with Sadayasu?, if so I would be interested to hear it.