I had been eyeing the Arca D4 for a few years but was discouraged by both the limited availability and the price. When I saw Charlie Cramer's video (it's HIS fault! :-)), I could resist no longer and went for it. What a pleasure it is to use this device. It's too bad I no longer use a 4x5 or even a medium format, but my Sony seems pretty happy perched on it and when I compose and set it, it STAYS! I'm selling my venerable Arca B1 and probably my Acratech as well. This is my last tripod head and it even works tolerably well on my Gitzo 1 series though it is clearly happier on the Gitzo 3.