I will try and remember to bring my iPad home from work on the weekend. To be honest, I only tried it once, by pure chance, as my iPad was home for a screen protector install and new case that was Amazoned along with the Fenvi. I enabled screen screen mirroring to my iPad and iMac, moved the window back and forth between them all , said neat, and that was that. My main goal was to have it work with my iMac so I can swap it with my second monitor on my desk, which it did and works like a charm.
As for Universal Control's performance, it's kind of 50/50 in terms of what's optimized/prioritized. Moving the mouse pointer and/or a window between the devices will be laggy (or perhaps low frame rate?) on the extended device, regardless if it's extending/mirroring the screen or using keyboard/mouse mode. However video playback is smooth with audio being perfectly in sync (and sounds great), even if the extended device's audio is set to the host device's output. What's cool is even when both my Hack' and Mac are not using any of the UC features, I will get an icon pop up in the dock with a little window in the top wight to denote what's active on the other system. It's amazing that a Hack' can seamlessly integrate itself into the Apple ecosystem!