(Review written from a phone. Typos may abound.)

Hm. I, too, can write 20k a day when all I am doing is rambling and repeating the same thing a thousand times.

Less than 10% of this book was actually useful common-sense advice in actionable lists.

35 to 40% of this book was excluaively  the author going "I write over 20k a day. Not many people can. I do. I get paid lots to do it. I make a lot of money ghostwriting. I live on an island and get paid a lot. I'm looking out at the ocean, from my house in an island. Because I get paid a lot. Also I record several podcasts a day and have jobs waiting for me all the time, I make a lot of money off those jobs. In my island. Where I write fast and make money. And I'm dictating this book. From my dock. In my island. Did I mention I make a lot of money ghostwriting?", And then some more was peppered through so I lost count. That was just how far I got with my kindle tracking it before it stopped being full chapters about his awesome life and began inserting that into what should have been useful advice.

The rest of the book was him rambling in between what should have been the meat of the "20k system" and repeating himself over and over.
Give it a hard pass. It's basically "research first, outline, create a writing habit and remove distractions."