[bdcravens]

> it's comparable to about 100k invested

When investing you typically can retrieve your original investment at any time.

> £6k for the first 90 days > Let's be conservative and you can get 7k/year out of this book

Keep in mind the author doesn't make that money, but rather, is paid a royalty. The author said they've earned more like $1100, and they expect around 1-2k a year, not 7k: "I am hopeful that in a couple of months this might lead to a passive income of $100-$200 per month for a while."

> author says it's more or less evergreen

No, they acknowledge the book likely has a shelf life: "...with all things in the tech world I imagine someone will write a newer book on the same topic in the not so distant future or perhaps some of the technologies mentioned will update substantially and my book will no longer be up to date"