The book shows how to do basic operations in all three such as filter, map, flatMap and reduce. It also shows what Test support they have. Also, the book covers what is special and different about each framework, how to handle errors, etc.
Also, for each one the book shows implementing how to an application using that framework and its integration with another framework/library. RxJava in Android, Reactor with Spring Boot, and Akka Streams with Akka http.