Nothing in their current offering seems like a moat to me, not in the sense that the word is usually used. Scaling a bunch of human contributors, and enjoying some modest network effects from that, could have been a moat. But then LLMs got invented.

If they want to make "the best way to learn stuff" truly general (e.g., calculus; coding; dating), and they had a secret sauce that differentiated them from the other players in those spaces, then I'd be very mildly interested -- still seems like learning chemistry or whatever could improve by an order of magnitude, and I'd pay for that. That's a tall order, though.