My complaints with the book: (1) it is not coordinated with the CDs; and (2) the phrases aren't written in Thai. You might value Thai writing sooner than you think. It's an alphabet, only about half of which is used most of the time. That comes to about two dozen consonants, and there's no upper/lower case, so the writing is within reach. Ironically, the tiny smattering of Thai writing in the book includes the Thai numerals; that's a waste because the Thais themselves use western numerals most of the time.
When you factor in what your time is worth, the *price* is not relevant. Pimsleur costs a bit more but is absolutely the best in my opinion: there's Conversational Thai, plus at least two others offered here on Amazon. Just search for "Pimsleur Thai."
And I don't mean to be a nag here, but keep in mind that even with the best materials money can buy, you can't buy the practice. You have to invest some quality time.
One ramification of no Thai writing is that you can't share this with your Thai friends when you're over there, unless they can read English.
The quality of the CDs is excellent. A professional British narrator says the English parts and I find it quaint and elegant, as if Terry Thomas is the instructor. :-) (Native Thais speak the Thai parts, of course.) They went so far as to include sound effects, e.g., for the how-to-talk-on-the-telephone part, it sounds like the person answering the phone is really on the line.
The book would be *utterly* useless without the CDs because Thai is a tonal language. Many one-syllable words such as "dee" and "cow" have several distinct, unrelated meanings depending upon tone. If you raise the tone at the end of a sentence in an attempt to make a question out of it, all you've done is change the last word to an unintended word, and you will only get blank stares. Since the phrases are only transliterated in Roman characters, you don't have a prayer of telling how to pronounce them from the book; they're mere memory-joggers for the sounds you memorized from the CDs.
Also check out the Language/30 cassettes. The Language/30 booklet can fit into a pocket and it has Thai writing, so you can tote it and just point in it to communicate without memorizing anything --an option well worth considering if you're just going on a vacation!
Whichever course you choose, be judicious about what you memorize. You don't need elaborate sentences such as, "I would like two bottles of Pepsi" when you can just say "Pepsi." You needn't memorize "Is it possible to have these clothes washed?" --because when you walk into a laundry and plop a bundle of clothes on the counter, it's obvious what you want. You only need to understand when to pick them up, so spend your effort learning words like "tomorrow," "day after tomorrow," "morning," etc.
If you're serious about proficiency, try Benjawan Poomsan Becker's fun "Improving Your Thai Pronunciation" CD. When in Thailand, pick up some of the cheap drawing books that Thai preschoolers use to learn their own alphabet.