I've studied foreign languages since the Nixon administration and even I'm forced to say that completing this course with good retention of its material in only 30 days is likely only if you're unemployed and have little else to do. However, if you're starting out in French, have studied languages before and know for a fact that you have a knack for it, this course is the best bang for the beginner's buck in terms of what you learn vs. how much you pay that I've ever seen. The amount you'll learn from this course dwarfs that of the entire set of Rosetta Stone French sets at well under a tenth of the cost.
Word of warning, however: if you've never studied a foreign language before, this course can be overwhelming for the language newbie. In that case, I'd recommend getting your feet wet with En Francais: Rapid Success in French for Beginners (Language Immersion Institute, book and 3 CDs, I've written a review of it). This course is best suited for those who have studied languages before and have a good aptitude for it.
As an aside, the German course in this series is also superb, and I've written a review on it as well.