This book is intended for those who wish to take the Japanese Language Proficiency Test (JLPT) N3. Originally published in 2013, the 2019 edition has been updated to reflect current versions of the JLPT. It is published by Sanshusha, a prominent language textbook publisher in Japan.
The book is divided into twenty-eight sections, which are designed to be completed one day at a time. They begin in the realm of grammar, work their way through vocabulary, and finally, kanji. Each section is accompanied by practice questions that target the features covered in the section. The final two days of the program are short reading comprehension practice tests, which serve as an overview of everything covered in the book.
If used as a month-long crash course for the JLPT N3 (which is its intended use), then it is probably a pretty effective book. The explanations of grammar concepts and vocabulary words are very minimal, and there are not a lot of examples of how each feature is used in real life, so it is probably not a great resource for more general, long-term language learning. That said, the way grammar features and sets of vocabulary are organized makes a lot of sense.
All in all, if you're ramping up to take on the JLPT N3, then this is a good choice.