I’m using it for my middle school child to accelerate math. I figured it was better than the in-class math enrichment classes that just rush through common core math curriculum, and cheaper I should add.
They are also WASC accredited if you’re in the US.
Yes, I heard about Math Academy, and will likely give it a try at some point. The price tag has made me a bit reluctant, but given the near-universal praise, I might bite the bullet.
You could also try beast academy and aops. We are huge huge huge (did I mention huge?) huge fans of them and have worked through pretty much all of their classes (1st grade through pre-calculus thus far).
Beast academy is around 15/20 a month and apps is more but you can just buy the book and work through it. Richard (the aops co/founder) has a ton of YouTube videos as well.
A third option is aops’s alcumus - which is a free math problem database. We use that a bunch as well and you could use it to figure out what you know and don’t know
They are also WASC accredited if you’re in the US.