True, this book is not meant to be an introduction to econometrics and I agree that you should already have a sound knowledge of undergraduate econometrics (e.g. at the level of Wooldridge). If you already know what OLS and IV are supposed to mean, then you are ready to read this book.
Anyway, the book does never claim to be an easy starter, but rather an "empiricist's companion". Thus, the book should be measured against the claim of being a book helpful for people who are doing research with actual data. Anyone who has ever read a book on econometrics knows that most of these books are actually written by researchers who are doing econometrics WITHOUT any data at all, or as if econometrics was not about data analysis in the end. I guess that's why most students have a hard time bringing the methods to the data (even if they grasp the theory). This book is different from most (actually all) other econometric books I know because it assumes that you mainly want to apply econometric methods to answer some interesting and substantive question in a convincing way.
Even though this focus is very different from the focus of most other econometric books, it actually mirrors what applied researchers actually do. This is true for labor economists most notably, but also for an increasing number of social scientists from other fields such as development economics, health economics, sociology and political science. For example, you will learn about regression discontinuity designs and quantile regression models. These methods are used increasingly in applied research. Nonetheless, "conventional" econometrics texts usually don't say much if anything about these methods.
Overall, anyone who wants to do serious empirical work and has the required background will find this book not only a very valuable resource, but also an entertaining one. This, I think, is more than you can hope for from a book about econometrics.