Mastering lambdas is the second book I've read about lambda. The first one, that i'll use for comparison, was "Java 8 in action" (which is about Java 8 in general, not only lambdas).
This one is written in the same precise style as the very good (and relatively little known) "Java generics and collections", of which Naftalin is a co-author. Some of the content (exception management, performance considerations,...) can't be found anywhere else. On the other hand J8IA is not as well written, but it covers one important technique that "Mastering lambdas" doesn't (using CompletableFutures with Streams).
Overall it's a great book. Also because it's so concise, it's not too thick and can be read in a few days.
This review is based on the printed version, not the Kindle edition (that i didn't try).