$39 is a completely fair price for your new knowledge, and comparable to what you’d pay for a printed book.
Any plans on having a printed book for sale? I’d be willing to this if I got a hardbound brick to sit on my desk.
Check out the “About the Author” page.
Do you plan to release this book as a paperback? No.
The author of the book is also the designer of the Triplicate typeface, which is beautiful. I cannot, however, bring myself to spend $89 for a font when Go Mono and Inconsolata are free. I know. I’m a bad person.
That being said, paying $99 for the book gets you a Triplicate font license, which I’m more willing to do. The book is worth paying for and there aren’t good free alternatives.
Triplicate is beautiful, but I don’t think I could ever use it for typesetting code though, it’s almost too beautiful for that. I’ve been using Fira Code Mono for my code lately and loving it.
Triplicate is very nice but I do tend to switch my monospaced font periodically (typically when a new hotness catches my fancy), which puts me off spending any money on one. Like @basus, I’m also currently using Fira Code Mono :)