I have the newer model with the screw device to secure the rail/plate. Great tripod head. I am not sure but I think that the price for a new item is actually cheaper for the Z1.
resummerfield, I am thinking of using my Z1 ballhead with an older model Arca 8x10 camera. I have both items but have not had a chance to use them. In your experience, is that viable? I really don't want to pay the money for a B2 if I don't have to. Thanks.