I've used it, and it is worth it, especially if you want to ride the rides multiple times. The hardest part on some of the rides is finding the fast lane entrance. In many cases (especially on older rides), you need to enter the exit of the ride. There are usually signs, but they can easily missable.
If you are going during a busy time, it is usually worth it. Usually they do not even offer it during a non busy time.
A good reason not to get it, is if you can get in the park at rope drop, since you should (except on the busiest days) be able to get through a lot of the rides in the morning, take a break during the day, and finish off the rest at night.