It is subscription based and you get access to all of the courses for a single price. To gain maximum value, you will need to use the platform regularly. For me it is worth it as the content is good qquality content and it suits my learning style. Work through problem solving and developing intuition, often through visual aids and everyday experience.

The math and science subjects I'd say is most mature, and has the most content. thereafter one can practice more from textbooks or alike to really go into the depth and expand on the mastery.

FB recommends it to prep for interviews with probability/stats requirements (Product/DS/Analytics)