It's been a while since I've used it, but Touring Plans uses TWO methods - their own predictive modeling based on past info, and guests using the app to report the posted and actual wait times. I don't think they were feeding off the data that MDX was presenting, but that may have changed.
I know there was one site that was scraping the MDX info somehow and posting it "live". Don't know if it still does. But even then, it's a bit of a different beast - in IT terms, the data is not "time sensitive" - I don't really need to update it every few seconds, forcing a query of the server and thus more load on it. I could grab it every 5 minutes, say, and then everyone else gets the info from me. That's only 12 hits to the servers an hour. Not even noticeable to worry about. And it was probably a "cheap" query - just getting the data already gathered in a cache table (at least if I designed it), as opposed to having to query the various systems for their current data.