I have been using this series quite often, especially with my students who like studying Japanese in depth.
Since the explanations are all in Japanese, they require a lot of patience and time.
I wouldn’t recommend them for people who found N3 or N2 a struggle, but if you enjoy learning grammatical structures, they are very useful.
If you have taken the JLPT N1 multiple times but haven’t passed yet, I recommend going back to the N2 textbooks. This may feel like a backward step, but it is an important process. Based on my experience, the students who barely passed N2 may not be ready for N1 level study.
When I take the exam, usually once I pass, I don’t want to see the textbooks again! So if you are like me and don’t like working on the same book again you can get a new one, but it is better to go through the N2 book one more time.
Anyway, the exam requires tactics, like a technique so if you can’t pass, it doesn’t necessarily mean you are not at an advanced level. I believe that continuing to revise and learn still helps you a lot. Please continue your studies without stressing yourself too much.