joamo Your experience thus far virtually mirrors mine, sans the inclusions. My stones are very clean but my results are very similar to yours. Chalky feel is an excellent description for this stone. Much more so than the slick hard guangxi.
One difference is that I have been able to get slurry with my "12-15k" but quite honestly I dont like the feel of it. The slurry off of the coarser stone feels much smoother cutting to me.
The jury for me all around is still out as I really only picked up the lower grit stone for kicks and dont need it so my hopes were more for the higher grit stone and im just not there with it yet.