Naniwa diamond whetstones are splash and go hard semi friable resinoid stones using diamonds as the abrasive that are excellent at cutting difficult steels. There is a 1mm thick layer of resin bonded diamond abrasive over a 5mm aluminum plate. These wear very slowly due to their hardness so they will last a long time despite the thinness of the abrasive layer. These stones have a harder feel with less mud generated during work than the average Japanese stone (although they vary a lot in their hardness).
After testing these on a big variety of stones we found that where they shine is on super wear resistant high alloy steels (looking at you American powder metals). Easier to sharpen steels don’t seem to get worked very fast, they do not have the feedback of a stone that generates more slurry. However on hard wear resistant steels they are noticibly faster than most whetstones and we found it easier to maintain flat bevels with the reduced amount of work needed, these compact stones would make excellent companions for hard powder metal outdoor knives in the field.