This is like having your own personal proffessor you can ask unlimited questions of at anytime, even 2 am. It has a lot of features, including sending you daily email mini lessons if you want!
The quality of the output and the way it's structured is very good too, better than I expected.
The thing I'd like to see in the future is the ability to train the AI on your own data and use that data specifically when you want to. Certain types of information are more idiosyncratic than, say, physics. For example, maybe I want to learn to write, but I don't want generic writing advice, I want to learn from Hemmingway specifically.
Even so, this is still a great deal as is. You can go as deep or shallow as you want in a subject, and then test your knowledge. No-brainer for people who need or like to learn I'd say.