The course is well built intelligently, as it immediately confronts the main difficulty of the Khmer pronunciation including short and long vowels that can change everything. For example in the course 2 knyom TIAP tia: p (read: me catch sparrows).
Everything is very well explained and gradually. The book is of high quality (too bad it's only Assimil pocket size, but the size of the collection). The transcription system is understandable.
One complaint (which can be done with other methods) is that it introduces too early the notion of politeness. For example, you can say "I" in different ways, while "knyom" is the first word that you learn on the spot. But when you start, you want to use the vocabulary as soon as possible and I do not know about you, but I have not had time to speak to the King or so monks deference, it can wait Lesson # 99 ... Same for some expressions for which there are more modern versions, but it has its charm to be laughed by the locals.