This short book, written by Jamie Allen, contains number of advises for Akka developers. I believe that you should be already familiar with Akka framework before reading the book, because the author assumes that you already know how to use at least the basic features of the framework.
First chapter of the book discusses the approaches to designing actor based applications. It's hard not to agree with the author about the presented ideas, but I think it's something that most Akka developers already know.
Effective Akka's second chapter presents two quite small patterns used in real world applications. I liked the first one, but the second one I consider a tip instead of "pattern" - like Jamie called it. Application of the pattern are presented with unit-tested source code, which is definitely a plus.
Third chapter (the last one!) presents general advises when using Akka, but I feel developers should be familiar with them already as these advises are not much different that general programming / designing rules. The only difference is that here Allen show how they are relevant to building actor based application. You will also find here ideas for creating systems with resilience and high-performance.
In conclusion, I'd like to say that the book seems nice to me. On the other hand, as Akka developer, I'd love to read a book that would push me on two levels higher in building actor systems, and this book left me a little bit disappointed in that regard.