This is not a pleasant book, and Michael Cohen is not a pleasant character. He comes across as a crook who finally got caught, and is now desperately trying to redeem himself through abject mea maxima culpas. Consider him a rather unreliable narrator.
Nonetheless, he provides insight into what it's like to work with Donald Trump. To the extent that it chronicles the Trump presidency, obviously this book will become obsolete on Jan. 21, 2021 at the latest. But it also provides some insight into what it's like to live under Trump's spell, to see him as someone worth admiring and fighting for. This, despite not just knowing what sort of person Trump was and is, but actively carrying out a lot of his dirty work. This part gives some amount of insight into the eternal question of how a Hitler or a Trump could have been elected, and how demagogues hold sway over populations.
If you don't want to buy the book so as not to give Cohen any royalties, by all means borrow it from your library. I, for one, found it more interesting than Bob Woodward's [b:Rage|53317913|Rage|Bob Woodward|https://i.gr-assets.com/images/S/compressed.photo.goodreads.com/books/1597575057l/53317913.SY75.jpg|81657197], which came out around the same time.