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Compared to what? They have a track-record of students not even old enough to be in high school yet passing AP Calculus BC exams.

Here in Taiwan, where I live, it's not that uncommon for people to pay 5x that price per month on supplementary math courses for their kids.

https://twitter.com/_MathAcademy_/status/1708542077695574292

Compared to Kahn Academy, which also has a proven track record, is free, and has been around for a long while.

If your time is worth even $1/hour, the "free" Kahn Academy option will be far more expensive than this program.

I respect what Sal Kahn built, especially in the early days, but it's just not anywhere near as time-efficient.

Is there any data to back that up? Just because it's a paid resource doesn't mean it's better.

The tool might be good but there’s also strong selection bias due to its price.

This is cheaper than lessons with a teacher, so it's hardly excessive. (Even if higher than other learning services)

It's not cheap. Given that it sounds like this is something you want to deliberately spend time on rather than just an app to use when you're bored it might be worth it but probably not so much if you can't use the knowledge professionally somehow.

If it works, it is a bargain