I used TGM for our last trip, which was last year. Now unlike others, we have not been 20-30 times, we've only been 5 times and not in a row. I found the information very helpful, especially since we go during the summer when the parks are the most crowded.
If you are going to order it, I would get it in plenty of time before your trip. Like someone else said, the site can be a little confusing to navigate, so it can take some time to get use to. But if you are a planning/information junkie like me... you will love it! I don't remember how much I paid for it, but it didn't seem like that big of an investment for what I received.