I'm impressed with the pricing of $19 early access / $39 final version.

I'm used to high-value books for professionals either being completely free,[1] or starting at $100. [2][3] It seems like a good compromise at that price.

[1] https://craftinginterpreters.com/contents.html

[2] https://www.refactoringui.com/#get-refactoring-ui

[3] https://www.amazon.com/dp/0262048434