I used the So-Matome books and found them effective paired with other material. (In my case, I had access to the JET program’s upper-level intermediate online course, which was dialogue-based and, I found, pretty effective.) After finishing that course, I went back and finished up So-Matome.
For N2, I’m doing the opposite: So-Matome first, and then I’ll grab Kanzen Master or another more detailed book for review. I think either way is fine. If you’re like me and benefit from having pre-structured material (a section and a quiz a day, in this case), So-Matome + something else seems like a solid approach.
The way I’ve structured my study, between apps like Wanikani and iKnow, and books like the So-Matome series, I don’t have to fuss over selecting my own material: I just try to clear out the app ques once a day, and get through a section of each test-prep book I’m working on (usually one or two at a time), taking notes into a Word Document for later reference. It makes study very automatic, very structured, and includes daily quizzing, all of which fits my preferences. It’s led to steady progress, though I should note I’m also in Japan, so I guess I can’t fully speak for how effective it would be without the daily exposure.
I also recommend building in reading and listening time no matter what materials you use. Find some easy Japanese-language news; read some manga or prose; watch videos with Japanese captions on, etc. And take notes on anything that stands out as being particularly useful for you while you do it. Really, I feel like no matter what, between apps, books, and native reading/listening material, the most important thing is just to have a set daily routine.
Last note – Grammar is fun! Vocabulary is rote memorization, but grammar is where you actually get to learn how to say what you want to say. It’s also amazing to watch grammar study opening up comprehension for you. You can always look up an unknown word on the fly, but unless you understand how everything’s fitting together in the sentence, you won’t be able to get the proper meaning. The logic of Japanese is so different from English, but consistent in its own way, that it’s fun just to start to get a lock on.