To save bulk I have been interested in the Acratech GP-ss ballhead lately. It takes a quick-release plate which has to be selected according to the camera. This is problematic for me because I use 5 to 10 different cameras each month and want something generic.
Manfrotto recently released the Q6 plate which is also Arca-Swiss type but is universal and actually very reasonably priced around $25 USD per plate which I would get 3 or 4 of.
Among press materials I found a statement saying the Q6 clamp accepts other Arca-Swiss plates but my question is the other way around, do other Arca-Swiss clamps accept Q6 plates? The design is similar but the wide top-part makes me doubt.