I think they are different beasts. The advantage of the Cube is that the centre of gravity pretty much stays above the centre of the tripod, which both helps in weight distribution and minimises refocus. Its a brilliant idea, though quite slow to work with, but fantastically precise. Combine that with a TSE lens and you're close to a view camera, even something similar to back tilts can be achived.
The d4 is rather a pan/tilt head whith the possibilities to finetune any settings by gears. It's much lighter and cheaper too. I ordered one once I saw it at photokina, took me 2 minutes to decide.
