I use this book for several months to revise my grammar and conjugation in my transport. Each lesson is a page, and related exercises on the right page, can be read, facts and self-corrected in less than 20 minutes. I was able to review most of the grammar points discussed at the Goethe Institute in recent years, and learn new rules. I can not recommend this book to people who want to improve in German, especially the students level B2 to C1.
