I have it on a docked iPad 2. I use a new iPad (gen 7) to mix. If I didn't have the new iPad, I would call it almost unusable. The lag is terrible, and some text windows don't display properly while naming channels.
I noticed a big slow down on my iPad 2 when I upgraded the ios to allow me to load MF4 and the X32 app. Before upgrading, my iPad 2 ran like new with no lag at all using MF 2.x.
The new $330 iPads are really nice, and mine runs super slick. I'm planning on getting another soon. I also want to upgrade to a Lighting tray but I cannot confirm whether Mackie has one that will fit the new iPad.