I have tried Math Academy after seeing a post here a few years ago (I think it was to Justin's blog? --- he's referred to early on in TFA).

Echoing what others say: it was very cool, went quickly at first, but within a few weeks, progress slowed because I just couldn't ingest the new information as quickly, even when doing two "blocks" a day.

It is superior to the free tier of Khan Academy.

I don't know if it's superior to textbooks and problem sets in a self-study capacity.

I found it better than the (highly rated) math education I partially received in HS.