@allemyr I have an Atomos Ninja 2, from the cheaper end of their range, and it mirrors the ML display, treating it as a focal plane. The result? All ML UI elements are in focus, and are highlighted by focus peaking. In other words, it doesn't work (for me, with 5D3 1.2.3) for focus peaking.
I know that the waveform, histogram and false colours work, but it may be reacting in the same (false) way; I haven't tested them. For focus, articulation and a backup recording, it's fantastic!