Vietnamese as a second Language 3 (VSL3) is the third book in a series of 6 that has been compiled and edited by a group of lecturers from the faculty of Vietnamese Studies and Vietnamese Language Program for Foreigners, of the university of Social Sciences and Humanities, Ho Chi Minh City. It is estimated that this book can be mastered in about 100 class hours.
If the book had a more accessible audio file, then it would be much better and its flaws more forgivable. The actual university that publishes it appears to only sell xeroxed copies with no CD. More important flaws are the lack of a glossary, outdated pictures, little everyday vocabulary, and too many drills. Their grammar explanations at the end of the unit are always too short also. If they incorporated them into their drills, it would have been a big improvement. Their cultural sections at the end of each unit were also very tangential to the main topic of the unit and really only serve to confuse the learner with additional vocabulary and foreign ideas. Those are important, but shouldn't just be shoved in. Lastly, there's not a single section on pronunciation throughout the entire book. Throw in some minimal pairs or oddly spelled words at some point, maybe even show how tones change based on their surrounding tones. I'd wager pretty much anything (related to the target language) would have been better than ignoring it completely.
In reality, I guess what happened is that the publishers/authors were aware of an obvious lack of Vietnamese language learning books, set up a format where each book in the series could be the same, and then published them. That's actually a great idea and a step towards how language books should be done and is something often English programs in the country lack. However, the actual setup itself is not that great. I've seen a lot of Spanish, Russian, English, and German textbooks that are just better for a lot of the reasons I stated in the first paragraph.