This book is amazing. I've bought many Teach Yourself books, but this book makes me want to go through it.
This book isn't built for colloquial speaking in informal formal situations. It's about being a tourist, but only for the first half of the book. The writers in this books seem to have decided to make it for people who want to be tourist, and people who want to become close to fluent. The first few units detail tourist situations like going to the hotel and getting letters. The subjects move to more advanced conversation, but as Swahili isn't that complicated in most respects it isn't bad.
The most notable thing that can be noticed about the Swahili language is the use of putting nouns into different classes. This is likely the most confusing aspect of the language. This means that they need to be taught very slowly, one noun class per unit... well technically two because the plural counts as a noun class in most cases. The language is easy besides that, with probubly the easiest to understand Verb system, that a three year-old could understand with little effort and a bit of memory.
I'd strongly advise this book to anyone who has an interest in understanding an African language (It could be useful one day) or plans on taking a trip to Kenya, Tanzania, Uganda, Rwanda, Burundi, or Even Southern Somalia.