Please check discussion from https://www.ozbargain.com.au/node/576726
Looks like historical low https://au.camelcamelcamel.com/product/B001TPH9CM?context=se…
Cutting Speed: Fast
Grit: Medium #800
Suitability: Max 60-64 HRC steels, can be used on softer steels.
1000 is also on sale $76.50
https://www.amazon.com.au/Chosera-1000-Grit-Stone-Base/dp/B0…
If you aren't a professional sharpener you can look at naniwa gouken arata, from what I've read/heard it is the same stone just thinner and cheaper.
From amazon japan you can get it between 50-60 which is a good deal