[huhtenberg]

The problem is that finding a postdoc that is also a good _teacher_ is a monumental task of its own.

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.

[ykonstant]

I have no experience with those platforms, so I don't know how deep the instruction is. After taking, say, a Calculus course there, would you be comfortable doing Spivak's exercises? If yes, that seems great.

[huhtenberg]

This is orthogonal to the instruction quality. What good is the depth of the material if the teacher can't explain it clearly and concisely?