I have not stoned with it yet. No need to right now, as my entire rotation is about as sharp as they are gonna get. Soft Cotton or linen (dry) with a light coating of this (powder) is awesome!
I believe that the pure powder is uniformly finer than the bar. Being a pure form you also have a lot more options as to how to use it. On the other hand if you can find it buy the bar. You will not be disappointed. Especially if you have a micro-chipping problem.
My initial results were on stainless steel, but carbon loves this stuff!
You can use oil or starch, but water tends to push it away from the honing surface.
This stuff is fine. No drafts. Be safe.