Make it hard, so you can control and maintain your edge geometry, assuming a flat secondary edge. And learn the grit comparisions of each compound. Decide if you want a toothier edge (leather ect) of a more polished edge,(paper cutting ect) 600 grit will leave a toothy edge above that will take those micro teeth out and make a more burnished edge. If you want simple, glue hard sole leather to a hardwood board, charge it with green compound on one end white or pink on the other. Green is roughly 600 grit, white roughly 2000 grit. For convex grinds like many head knives a slightly softer surface like a hard mouse pad or other neoprine, or a softer leather surface should be used as it will roll with the convexed grind. Often ill step down in grits Untill im using charged cigerette paper but thats for certian crazy sharp demonstrations and not suited for leather cutting needs.