The Smart Flex Bracket with Phase/Mamiya Plate has five main features:
Arca Swiss Compatible
The quick release plate itself and the bottom of the L are both Arca Swiss Compatible (Really Right Stuff also uses this form factor). In addition there is a screw-in point for non Arca Swiss compatible heads.
Easily rotate from horizontal to vertical without removing the camera from the mount.
Long/heavy lenses usually create a front-heavy balance on a tripod. Using the fore-aft movement you can move the camera to compensate for large/heavy lenses.
The same fore-aft movement allows you to mount the camera directly over the nodal point. When rotating from horizontal to vertical this point does not change.
This item is for a Smart Flex L-Plate with a Phase One / Mamiya compatible insert. This insert works with the Phase One XF, DF+, DF and AF and the Mamiya DF+, DF, AFD3 AFD2, and AFD. But other inserts are available for Hasselblad, Nikon, Canon and more.