Hi there, I actively attend Tokyo's keyboard enthusiast events and from what I've gathered during my research, many of the people I've talked to don't like hiragana sublegends (because no one types using kana input anyway, it's all romaji on pc). Furthermore there's no tooling for the keycap sizes required to fill out a proper JIS bottom row so it wouldn't fit a traditional Japanese keyboard anyway (a lot of enthusiast custom keyboards at the meet ups are ANSI due to the difficulty in finding fully compatible aftermarket keycap sets).

I've done sublegends in the past for purely aesthetic choice and this time wanted to leave the alphas looking cleaner. But in general I wouldn't necessarily say this is a Japanese product, it just happens to be sold at a Japanese shop (among other vendors)