I'm with Roger there, Kyosho diffs are some of the best and smoothest out there.
Always use as little grease as possible and the quality of the grease is of upmost importance. I exclusively use AE Stealth lube.
As for the diff being hard to set, I disagree as well, probably what's hapening is that your slipper is way too tight. My diffs are really free and don't slip, proof of that is that I could pull wheelies on carpet with the ZX5
