People complain about his book a lot, as is their right, but the finger tapping experiment was actually conducted by Walker's team and the scientific paper[0] has been cited over 500 times.
I found these critiques soon after reading the book. However, there are many other researches cited in the book and I would take them on face value for the not very scientific but somewhat valid (for me) reason of personal experience.
I got into the habit of all night slogs right since high school and it persisted till recently due to the pressure of sticking to deadlines. So I could relate well to several experiments cited in the book.
Considering we do not know nearly as much as we ought to know yet, I would rather err on the side of caution and give far more importance to sleep than I have previously.
[0] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC202318/