It’s only a few years old, so it’s hard to find reviews about it. But I’ve heard they’re good? Each textbook is catered to a different JLPT level.
I learned with the N3 one as my main book for N3 and passed it with full marks. It’s pretty good, especially for the price, since it offers some light reading, grammar explanations, and some multiple choice excercise questions with a listening part. It covers all bases you need for the JLPT. It is pretty short though, so the grammar explanations can be lacking sometimes and nuances can get lost. I wouldn’t recommend it as the sole source of your learning but I feel it is a great book, that gives you an overview over what you need for each JLPT Level.
I can recommend this book. I used it for N5 preparation. The things I most liked about the book are the brief grammar explanations and the tables. I like seeing information organised in tables. If you also like tables, go to a book shop and take a look inside this book.
There is a practice exam at the back of the book. I think the real exam was a little bit more difficult. I started my N5 prep with this book. Then I went on to several other practice materials.
If ordering online, be careful about the language of the explanations. The book is translated in multiple languages. I don’t want you to get stuck with the Vietnamese version if you wanted English.