I've been on this tour 3 times (over the past 6 years or so). The tour is very pleasant and educational, and I like the fact that it's about an hour; it doesn't take up half the day or longer, like some of the other tours at WDW. It's not expensive either. (Note: if you purchase the Birnbaum's Guide to Walt Disney World, they usually have a coupon in the back of the book, that gives you a discount on this tour. Haven't picked up the 2016 book yet, but all the previous years did include a coupon for this.)
Every time I've wanted to go on the tour, I've just walked up to the desk (near Soarin') and had no difficulty signing up for available tour times that day. Each tour I've taken seemed to have the maximum amount of guests they could accommodate, so the tours do eventually fill up each day.
