Funnily enough, Fanpass works fine for me if I'm watching it on my iPhone/iPad but as soon as I airplay it, it becomes buggy and wants to buffer every so often. It's the only service I have issues with Airplay on. I've recently been watching US Netflix via airplay without an issue.
How odd! I'm airplaying from an old iPad 3 to an ATV4 without issue. Hanging out for Fanpass to make an app for the ATV, though. One less device to have to deal with.
When Lightbox and Fanpass come out with Apps for the ATV4, I'll upgrade me ATV3.