Have you tried it? And does it work? Not doubting your word, but would like something on hand that is more more reliable than the various 'debated' burn cures such as butter, cold/hot water, and other untested remedies.
There was a jar of it sitting in our Kyoto kitchen for years while our boys were growing up. I never had recourse to use it personally, though it was used on the boys (who suffered the usual minor burns a few times) with good effect. I don’t know how widespread its use is/was in other Far Eastern countries or even throughout the rest of Japan. In Kyoto though it has a history going back at least 100 years.
The most interesting example of its use is an account of it being used on an x family member (now in her late 70s) who was badly scalded as a child on the shoulder and down her arm. The liquid was applied and there was no subsequent scarring – except for one small area that had accidentally been missed.
The Japanese cucumber is slightly different to its Western counterpart so I don’t know if that would make a difference. I also remember that the stuff in the jar smelt very strongly indeed.