It will probally work out about the same unless you do a mouse hack for the trackball.
The main difference, if you want to add a spinner later, you would be able to connect it to your minipac and the minipac would handle both devices, disabling the one you are not currently using.
(much easier config, no multiple mouse devices.)
Also with the minipac, just 1 usb cable for buttons and trackball.
Later,
dabone