I’ve met a few students of this textbook system when I was on exchange and my impression was that they were very skilled at Japanese for the amount of time they’ve been a student and what they told about their seniors was they pick up kanji fast, since they already know the words.
The big problem of course is that it is completely incompatible with other schools. Where do you place them when they go on exchange? With the n3 or n5 students?
Anyway, I always thought it was interesting that the exact antithesis of RTK* exists and works.
*RTK or “remembering the kanji” is a system that teaches all kanji before student learn their first word. It’s quite popular online as it lends itself very well to solo studying.