I have a Rev-1 IPAC a(and need to upgrade its chipset). It's a beautiful design and allows for easy configuration and reconfiguration of harnesses. I do wish it had spinner and T-ball support, but those are easy to add...
Really, you only want the Mini version if you have very limited space and hard-set controls. If you ever think you'll want to add additional controls, or want to reconfigure things, the full version is the way to go, and if you want 4-player support, you want the IPAC-64 (or however many inputs it has). interestingly, mine has an unusual number of inputs: No longer sold like this.
Once I do a modular C-Panel, i may get an IPAC-64 for extra inputs and wire everything via some Molex connectors, but the basic version is really a bitchen' product. The box header is also something i''d avoid, as it makes it hard to repair if you pull a wire; you can also jumper more than one button to a single input on the full version, which is useful if you have a few games (or an emulator that uses different keys that MAME doesn't use). You can jumper two buttons to a single input and pressing it generates both at once (e.g. 'Shift' AND 'Z').
I'm not sure if the Mini version can be programmed either, but don't take that one faith, as I'ven't read its documentation in full. -GG