after returning 3/4 wireless mighty mice for scroll down messing up, and having recently switched to the logitech vx, i recommend buying the vx and just selling off the wired mac mouse or keeping it as a backup incase you run out of batteries (so usb).
Having said that, the first vx i bought had a faulty button, and this second one wobbles and rattles when i move it when in hyperscroll mode, but thankfully i dont use hyperscroll and its fine in the normal scroll mode - still might return it, not sure yet.
Also, all VX+MX mice eventually lose hyperscroll feature due to rubber expanding and dragging on the apparatus, resolved by either returning it back to logitech (and i think paying shipping) or snipping the rubber (2mm) yourself, which apparently works for everyone.
The difference is, i would gladly go through the effort for the vx because it is the best wireless mouse ive used in terms of ergonomics, response/lag (my might mouse wireless had terrible interference) and just all round being a great general-use (ie not gaming) mouse - if only we could switch between normal scroll mode and hyperscroll mode with a click like the MX as opposed to flipping the mouse over and turning a bit of plastic. However the MX has its own problems with battery not recharging etc.
hope that helps someone...