I don't know that they change every month, but the offers are not always the same. It would be hard to know whether waiting will get you a better deal or if waiting will cause you to miss out on a great offer. In February or March, UCT was offering a "buy 3 days, get 3 more free" on park hoppers. Those were perfect for my Sister's April trip. That offer still appears on the Mousesaver's link, but who knows when it will be gone. It's sort of like buying air -- when you find a price you're comfortable with, buy it. You'll definitely save over the WDW direct pricing.
I've ordered from UCT 4 times and have recommended them to several friends and family members. We've all had great experiences -- no complaints.
