https://www.reddit.com/r/slatestarcodex/comments/dwtr0m/matt...
The overarching point that guzey makes is "the book is not scientifically sound, despite Matthew Walker plainly stating in the introduction that it would be". Arguing that Walker's claims are "hyperbolic, [but] within reason", that it's ok because "it is a book intended for the public" or that all this is "justified by the important message he is trying to convey" is completely besides the point! That may all be true and not change the needle one bit on "scientifically accurate".
Making up unsubstantiated claims to ""convey a message"" in a book and then later citing the book in your own scientific papers is the exact opposite of academic integrity. Hence my advice to take Walker's work with an appropriate grain of salt.
See e.g. https://news.ycombinator.com/item?id=21546850
That is not to say he's wrong on every count, but take what he says with a huge grain of "might have been invented/fudged and then cited from and by himself" salt.