First, manage your expectations. Assimil Khmer is not Duolingo. There are no gamified leaderboards or push notifications.
I spent a month with Assimil Khmer. Here’s my honest take. assimil khmer
Assimil Khmer is the best tool for the intermediate beginner. It fails as a true "zero to hero" course because of the script difficulty. However, once you learn how to read (even slowly), this book is a goldmine. First, manage your expectations