Their team of mathematicians have created a curriculum from k-12 to a bachelors in mathematics.
If you want to learn some math and are willing to fork over $50 a month, my advice is to find a competent tutor online*, tell them what your goals are, and work with them to produce an evolving, customized mini-course.
Have them pick material suitable for your goals, work through it in-session together so they can spot gaps in your knowledge/technique and make progressive problem sets to cover those gaps, and so on.
*A local tutor would be better, but I presume they will be prohibitively expensive in the average HN user's location.
But how many hours of tutoring will 100 bucks/month get me? Maybe 1 hour per week.
Compared to an online platform that's being used by a ton of people, has lots of reviews and recommendations and that is, presumably, actively optimized through a feedback loop, it's an easy choice between the two. Also, a platform removes the friction of cancelling the engagement if the need to do so arises for whatever reason.
I mean, if someone I know points at a postdoc and says "this guy is excellent", then their recommendation will prevail. But chances of that happening are next to zero.
The math thing is just a side project at the moment to try to see how it works for other fields. I am primarily using this for music. I was hoping something like this existed already, but all the solutions are either very specialized like this one or do not support dependencies as a core feature, like Anki. Had Anki supported something like this, I wouldn't have needed to make my own thing.
And yeah, I don't think Anki gets a lot of support. I am an open-source maintainer myself, so I know that story.
I have two children and I was glad that teachers are willing to use new tools (I never asked if they were forced to use them, but I assume not because each teacher seems to use different websites). I'm sure some kids still get bored, but they can let the ones who enjoy math practice at their own pace and provide special guidance to them while still spending the majority of their time helping those who need it.