Koki told me the same, that they are the same knife. Yet the ones that I got, I got 5, 2gyutos, 2 santokus , 1 suji, (for the kitchens I cook I dont need sujis that much), all have very nice even grind, are quality knives with very nice finish. Not mirror polished, not rounded spine, but then again not sharp spine as well.
I have to explain this thing about the spine. I am a pro cook, and if I happen to do preparations, I use knife for hours, and cut in a shift more than what a home cook cuts in three months. Some square spines are not bothersome, and you don't feel like smoothing them(like Masahiro Virgin Carbon 21cm), while others are very sharp and you have to ease them(like Masahiro Virgin Carbon[beastly knife, for werewolves] 24cm gyuto, Gekko[most square spine ever, yet amazing knife] 24cm). Some are rounded and wide, which is blessing(like Ryusen Tsuchime 24cm gyuto), and sone are rounded and thin-feel comfortable-like Ryusen Blazen 24cm gyuto.
The Hiromotos 24cm Gyutos with metal bolster I have, spine is square, but not the most square you can find. Some at pinch grip might find it bothersome, I find it tolerable. If you hold the knife from the handle, with pointing finger over the spine, it is more comfortable than rounded spine.
It is not a luxurious knife, but this isnt the philosophy of Hiromoto knives. The gravity is in the blade and to be functional.
You see it live next to Blazen and Hiromoto AS(outstanding knives both-great cutters), you understand who is the boss.
Very intersting is the small Hamon. I have analysed it at a previous post. They are made by Master Nagao himself.
The santoku is not in metal bolster version.
There are two santokus. The rosewood handle- santoku profile, wide blade, and hand sharpened in the stones by Master Nagao himself.
The other(from which I have two), has a light brown wood handle(lighter colour and more beautiful than the beautiful honesuki handle), has a hybrid santoku-gyto profile, which you can use both as a santoku and as a gyuto. It does not come with a hand sharpening in the stones.
All knives that I have, have even grind.
One Hiromoto AS, the 20cm gyuto, had uneven grind out of the box, yet was amazing cutter as it was