I didn't read every word in this book, but I definitely did refer to this book a lot, especially when I couldn't understand some of the parts I read in the Institutes.
A very useful tool. In reading the Institutes it can be easy to loose the forest for the trees, this helps you remember where you are in the context of the book as a whole. In no way is this "cliff notes" version of the Institute, but rather, it is a road map. I would suggest using this alongside your reading of the Institutes. It also contains several helpful diagrams and charts.