We got a regular Sunpass earlier this year and we live in northern IL. It's not only great for going to Disney, but also to the cruise ports in Ft Lauderdale and Miami (we hate to fly in or out of either - way too many people when all those ships have all those passengers disembarking and embarking) and it can be used on the bridge to Sanibel.
We got it not for any money savings - but for the convenience of not stopping in line to pay a toll (don't know what takes some people so long to pay a toll). We looked at the Sun Pass mini, but it has to be permanently attached to the windshield so you can't use it in a rental car (for the very few times we fly to FL - it's usually cheaper to drive than to fly and rent a car). So we opted to get the regular unit.