As a pro freehand knife sharpener, good whetstones are critical and I’ve settled on a few brands that I use daily, 6 days a week. Diamond stones have become very popular over the last decade in Japan and Naniwa has produced its version. I’ve used it on many hand made Japanese knives and it really is awesome. It’s aggressive, it feels like it’s doing what I want it to do, remove fatigued metal efficiently. Don’t worry, it’s not going to be ripping steel away like a grinder that’s out of control. This stone is exactly what I wanted it to be and it very likely will not need flattening. It’s 1mm thick but I guarantee it will last a very long time, longer than my synthetic 400 grit stones. I also sharpen every day so if you sharpen your own knives then you don’t need to worry. For the ultimate set up, follow up with the 1k NP Diamond stone. I’m very impressed and it takes a lot to impress me when it comes to water stones.