He means there's a lot of low hanging fruit left.

There is as much "low hanging fruit" left as in mathematics, economics,control theory,analytical chemistry and so on. Like the proverbial "100 dollar bill in the sidewalk" joke, any truly impactful, low-hanging fruit would have been taken eons ago. PhD dissertations, postdoc applications and tenure case presentations would love to use them.

While Anki may not be nice-looking, it's incredibly easy to use and free.

It's a very simple flashcard program. What is so hard about it?

Anki is definitely incredible! But it's in no way easy to use once you do anything more than a few hundred simple cards.

Just take a look at this video, and the apps ui, and tell me this isn't a clusterfuck: https://www.youtube.com/watch?v=2Y35WiKNbCU

So yeah, for a simple flashcard app, it might be easy to use, but if that's all you need there're better tools.

As for it being free.... Yes, and that bothers me. I would rather pay $$$ for a great product than use an okay one for free.