I started using this book (self-study) after having completed Genki I & II. At first I was quite sceptical of the book because the jump in difficulty was quite large from Genki, and there weren’t as many tasks to do in the workbook for the grammar points. As a result I felt that there wasn't much of a potential to actually progress in Japanese from this book, compared to Genki which was almost like a catch-all solution for learning.
However, after coming back to the book after spending much more time actually immersing in Japanese (reading + listening + more Anki SRS), I suddenly felt that the book was much easier. Then I realized that is just the nature of language learning in general, that in order to progress beyond the very limited Japanese in Genki II one has to actually start spending time with the language outside of grammar books.
With that in mind I think that this is a very good book. The chapters introduce different types of text - biographical articles, recipes, transcripts of discussion, etc - accompanied with new grammar points. Compared to Genki the grammatical explanations rely more on Japanese itself rather than being word-for-word translated from English. The examples given for each grammar point are entirely in Japanese at this point, and there are also smaller grammar explanations which are entirely in Japanese, which certainly aids in learning. There is also explanations of things like writing styles in articles, emails etc and information about differences between spoken and written Japanese. I also liked the brush-up chapters at the end of the book which explains basic grammar points in a more nuanced manner, like は/が as particles, conditionals and passive/causative/passive-causative grammar. After this book I can confidently read/watch slice of life moe shit.