It's a must read book for every tester, independently if he is a newbie or experienced tester. Jonathan guide his explanation on the automation pyramid in a upside down way, and I believe he is right. For testers it is a faster learning because they are used to working in the UI layer. But the author also explain really well the another layers in detail and with practical examples.
For developers in a agile team is a must read book too, because he show with some practical programming exercises in unit layer and mocking.