Chris Rodda explains the rationale for giving the book away for free here:
Do Well By Doing Good science blog post.
Here is a direct link to the book:
http://www.liarsforjesus.com/downloads/LFJ_FINAL.pdf
The book seems to be a rebuttal to the "Christian" right wing's various unfounded assertions about how the USA was established, how it developed, and how it should be governed now and in the future. I admit I just got it myself and haven't read it yet, so this isn't any sort of endorsement; I have no opinion pro or con at this point.
But if you're interested in the political power wielded by right wing Christians, or the Evolution/I.D. debate for public schools, or "In God We Trust" "One Nation Under God" and other overt religious slogans in governmental life, I think this book will probably have something for you.