Víctor
If you're looking for a good book to review the grammar points for the JLPT N3 exam, I think this is a good one. It's not flawless though. Let me explain.
So, the elephant in the room: yes, the grammar explanations are missing. So... yeah, a book focused on grammar is missing the grammar explanations. That's annoying, isn't it? But listen, I've also tried the Shin Kanzen Master N3 book, which has grammar explanations for each point, and I could not finish it. And I've finished the Nihongo Sou Matome. Why is that?
The thing is that the Sou Matome series are great at organizing your study sessions. They divide the grammar points in daily lessons: from Monday to Saturday you learn 3 or 4 grammar points each day, and on Sunday you take an exam about the week you just finished. This goes on for exactly 6 weeks.
If you're self studying, you'll probably know that sometimes you spend way too much time thinking about organizing your study (sometimes, even more time than the proper study itself). That happens to me. So, having a book that do that thinking for you is fantastic. You only need to focus on studying each day, and before you know you'll have finished it.
Maybe you'll need a grammar dictionary next to you, though. Because of, you know, the missing explanations. I'd recommend the Handbook of Japanese Grammar Patterns (https://www.goodreads.com/book/show/31700479-a-handbook-of-japanese-grammar-patterns-for-teachers-and-le), 99% of the grammar points are there.
If you're good enough at planning your study lessons (or if you enjoy doing that part), maybe you'll do better with the Shin Kanzen Master series. For dum-dums like me however this was great. I'm already starting the Reading Comprehension one next week.
