What is your opinion on "Powerful Sleep - Secrets of the Inner Sleep Clock"?

Digging around my bookshelf I found a copy of “Powerful Sleep – Secrets of the Inner Sleep Clock” by Kacper M. Postawski. I’m about halfway through it so far, and he’s made some claims that mostly consist of allowing yourself to sleep for 4–5 hours a day with more energy.

I have a problem with a couple of things in his book. Although he’s making claims that seem sound, he doesn’t really cite his sources very well or provide more evidence to back up his claims.

If you’ve read this book, what are your thoughts? Has it worked for you, or is this a fraud? Is there anything one should look for when trying to adjust a sleep schedule?