I've been using Tuple for the past year and a half or so, IIRC. It's just a really well done Mac app. One of those tools that "just works", is thoughtfully designed, and mostly just stays out of the way and does its job without doing anything annoying.

We don't pair program as a regular thing, but we have junior engineers on our team, and often when they need help, or we're working through some bit of architecture, etc. I'll pair with them. Tuple is the best tool I've found for doing that (remotely). I'm not teaching full time any more, but if I were, I'd absolutely be using Tuple to do remote 1:1 sessions for that as well.

Finally, I've interacted with Ben, the CEO of Tuple, and came away with a great impression of him and what he's trying to do.