I've been using leaf backs since the first one with live view came out. Back on the earlier models the video was better than on my Aptus 75. I'm not sure why they got worse but they do have a problem with contrast that the ND filters will help fix.
I shoot with both the mamiya and a sinar p2 and when I overlay a clients layout in live view with the 4x5 they are blown away. The only problem is they then want to match there pathetic layout to what the camera actually sees!!
I run a 2nd small flat screen montior on a long 20 foot cable then I drag the live view window to that monitor and can place it either on the camera stand or on the set. It's the best thing for focus and makes everything move much faster on a busy day of shooting products.
I just bought a Mark III and want to try the live view, I'm curious how it will compare to the Leaf.
Bruce