I agree with @zerohbeat here. I started using Bunpro just a few days ago, at N2. I failed the N2 test back in December by just a few points. So Bunpro is being quite helpful for me. At this level I’m already practicing a lot with native material, but passing the test requires you to memorize specific grammar points that you might not get enough exposure just from native material.
However, I also checked the N5 and N4 content from Bunpro and I feel it’d work better as supplementary content. If I were starting to learn Japanese now I’d use Bunpro N5 alongside a textbook, and ideally classes from a teacher.
I think that just learning grammar points isolatedly when you’re starting isn’t the best idea. Textbooks and classes are great in that they tend to present grammar points in a broader context, and you get to practice a lot. I think that for N5 and N4 it’s important to have more “handholding”.
So if you’re starting I’d recommend getting a textbook (and getting classes if you can), using it as a primary source to learn, then using Bunpro to keep practicing the content as you go.