Yep 169 feels a good compromise and 399 is a joke. Do it you know you want to . They are really good. However a lot of people here dislike them as you have seen.knives are generally ok - nothing major chipped or damaged.
Seems to be 3 options now - £99 / £169 and £399
I guess the £169 version is probably best as the £99 doesn't have the Ceramic disc, it has steel instead for the fine

They just won't listen. I'm also in the process of making a slow-speed diamond lap machine I'm just waiting for the variable speed motor to arrive. That's mainly for lathe tooling but together with the jig I'll be making it will surely perform well on knife blades. Obviously that won't be in the kitchen
The 6" diameter diamond plates I have range from 180 to 2000 grit and attach magnetically to the platten for quick change, even higher grits can be had for polishing.