Keep in mind that for hundreds of years, that guys have been honing razors, no one lapped stones. The “Dead Flat” razor stone is a relatively new obsession since the advent of internet razor forums.
Japanese knife and razor honers just raised slurry on the high spots, (ends and corners) to “flatten” raise slurry and smooth a Jnat stone face.
When recently Jnat’s became popular with razor honers, some long time Jnat honers claimed even using Diamon Plates to lap and raise slurry is a waste of good Jnats.
Bottom line, a stone does not need to be Dead Flat, just smooth. I usually give my stones a quick, lite lap with a diamond plate to break any skin a stone can develop and to clean, but you can do the same with nagura.
A quick update. I've been honing pretty much daily with this JNat and a second that I acquired from @musicman980 (Aiiwatani Kiita Karasu Koppa), which I really enjoy using. I'm starting to get a good feel for the slurry and I'm starting to find the edges to be both sharper and smoother as I learn the stones. My last honing was on a Titan that I was having issues with; I struggled to find an edge that was sharp enough, although I haven't tried it on my hard black ark yet. The last edge I had on it was from my Black Shadow, which was reasonably sharp and smooth, but I had some issues cleaning up my neck and a couple other spots with it.
Using my first JNat and a tomo nagura I progressed from a thick slurry to a medium, then a thin slurry followed by clear water, and I was able to achieve an edge that retain decent smoothness but was quite a bit sharper. I was very impressed with how well this stone was able to bring out the best in this steel. This is exactly why I wanted to start working with JNats and I'm looking forward to seeing what edges it can tease out of my razors as I improve my technique and knowledge of these stones.