How this founder sold his notes and built a startup for other people to sell their notes

https://www.oxbridgenotes.com/

I came across this founder on a HackerNews thread. Interesting how he made a business out of law school notes. Yes, it is that specific a niche and he makes 30K avg. a month. His product is not SaaS. It is a single download pdf. I would assume there are other niches out there.

Especially with Zoom classes where half the time everyone is on TikTok and not making notes, I think someone could adopt this to new niches :)

What do you think ?