Aloha, from Hawaii, I have experience with all three knives. Not too knowledgeable on heat treatment procedures, or if it will produce a finer grain structure, but from a real world experience all three knives are great. I currently own a 240mm KS, 150mm HD2 petty, (but i do want a Gyuto too) both great knives.
OK. Jack, few questions to ask you.
Do you mind the extra maintenance in having a carbon knife?
Since you are currently using German knives did you like the weight of the knives or would consider a lighter weight knife? The HD2 being the lightest and thinnest followed by the KS and than the Mizuno.
Do you use a steel on your knives?
What type of Stones do you use? Grit?
In my personal experience DenverVeggieNut is correct the white #2 doesn't really have the best edge retention, but what it lacks in, it is so easy to sharpen back to an amazing edge. The blue steel in the Mizuno will be great long lasting edge but in my opinion doesn't produce such a refined edge, but nothing too shabby, definitely much better than any softer German knives will. Finally, the HD2 in my experience with my petty the edge retention I can say is in between the white and the blue, but sharpening it (once trained to your style of sharpening) will be very similar to any high quality white steel. To answer your question about cutting harder root veggies, I feel that a thinner laser type knife will excel at cutting carrots and jicama, because of its thin and fluid grind, the knife just glides through the item without wedging. The only things I would not cut with anything really thin or flexible knife would be veggies such as Kaboca Squash, or other type pumpkins.
Had used all three knives (minus the HD2, but I do have a Ikkanshi Tadasuna 270mm Inox (Ginsanko Stainless Steel) but does compare to it very similarly Grind, Blade Shape and Weight) I still can't decide which I would pick out of the three. For my personal Masamoto KS, I maybe got a lemon or just bad QC (which they are known for) handle and install. For the handle, the d shape handle first of all totally does not even come close to what you play for, ferrule was not even close to being flush with the ho wood handle. Another flaw on my handle, was that it was not sealed with epoxy, water got in and rusted my blade, had to get a custom handle for it but love it now. Positive notes, the KS has an unique profile, somewhat of a shear shape which give you very little belly, having a larger flat spot.
Both, the HD2 and the Mizuno have the traditional blade shapes of most gyutos, Hd2 having a bit more of a flat spot compared to the Mizuno. Both knives have good quality control, personally I feel Konosuke has a bit better finishes overall.
To end this very long post, All great knives just comes down to the nitty gritty, of weight, ease of use, or even options. I know the mizuno will have the biggest customization's' on JapaneseChefknives, followed by the Konosuke HD2 with handle options, and the least with the Masamoto KS, maybe just ferrule options.
PS: Aside from the flaws in my KS, now it is a go to knife in my bag because it very versatile, thin edge but has a bit of weight to it so I don't have to use as much pressure. I also hope to have all three knives one day. If you are also considering other options I could make up a few other good suggestions that could be suit you too.
Hope this helped. Happy shopping.
Edited by Allen Lum - 11/3/14 at 2:53am