Significantly better than "Developing Backbone Edge", but still has a lot of room for improvement.
What I liked:
1.) Deep enough for a starter.
2.) Reasonably structured (there's not much jumping around).
3.) Quite a lot of space for testing.
4.) Sometimes it sacrifices depth for breadth, but each of "satellite" topics that were not must-have, but are included in this book was truly interesting.
What I didn't like:
1.) Editor did a good job in terms of checking typos, but (s)he skipped obvious errors in terms of understandability - in book's content there are some assumptions / rules / definitions that were not introduced in previous chapters.
2.) Flux description is fine in conceptual terms, but code to model correspondence is not described carefully enough
3.) Not enough real-life use case examples. Or rather - the ones that are provided are fine (and very well formatted) but they are too narrow - focused on very small code constructs.
In general - it's a good starter for React, but it requires additional sources of knowledge.
If you're looking for one-stop source instead, go for Egghead.io.