This product is the newer, 2nd edition, and is improved from the 1st edition. Make sure you also get the CDs.
I am a college student who went to Thailand for 10 days on a service trip. I only studied Thai for two months before I left. For one month, I used whatever online resources I could find, and for the second month, I used Colloquial Thai. I got up to about Chapter 12. I studied for a few (maybe 3) hours every day, and each chapter took me 2 or 3 days to get through. When I got to Thailand, I was able to say most things I wanted to say and I could understand a lot if they spoke slowly and simply. When the translators weren't around, I could chat with the villagers, order meals, satisfy my curiousity ("khun roojak the Beatles mai khrap?" - Do you know the Beatles?), and so on. I even made two speeches in Thai, on the spot, as a representative for my group. So, I am very grateful to this book.
Here are the pros and cons:
The transliteration system is easy to read, and the symbols marking tones are easy to get used to. The most annoying part is that they transliterate the sound we would call "g" as "k", and "k" as "kh." This is common in Thai transliteration systems, because the Thai "gaw gai" is slightly different than our "g", but it's a lot closer than our "k." Also, the way they transliterate Thai vowels makes sense, especially compared to Benjawan Poomsan Becker's system.
The goal of this book is to teach colloquial Thai, not written Thai. At the end of every chapter they teach you how to read and write some of the vocab from the chapter, but it's really not the focus of the book. You will be able to read signs (like "sukhaa") but you probably won't be able to write notes.
The vocab in each chapter is very useful. Every time I started a new chapter, I thought, "Ah, now they teach you the important stuff" -- but that's because they teach you lots of important stuff, and relatively little useless stuff.
The CDs are extremely valuable. Not only do they have all the sample conversations, but they have listening & speaking exercises. For example, they will play a conversation for you that's not in the book, then ask you questions about it, then tell you the answers. Or you will role-play the part in a conversation, "I'll give you the cues in English," says our friend John Moore.
The book itself contains a lot of useful exercises. It will ask you to talk about certain things, and then you can check to see if you spoke correctly in the back of the book.
Here's a complaint: all the conversations are between two adults of near-equal social status. When I went to Thailand, I was often speaking to children, who will call you "phee" (older brother/sister) and whom you should address as "nawng" (little brother/sister). I was very confused at first as to who this "phee" was, and they must have thought it funny that I called them "khun." Also, I tried to talk to a monk once and he sort of just ignored me, because I didn't realize that you have to address monks differently than ordinary people. So I never got to talk with the monks :(.
Anyways, this program is excellent, and if you want to learn Thai, get it.