Years ago, the car rental companies charged very high rates, as much as $10 a day for the length of rental even if you used it only one day but they have gotten much better in recent years.
Here is Enterprise's current policy:
$3.95 per usage day, not to exceed $19.75 per rental period. There is no TollPass Convenience Charge on rental days that you don't use a toll road.
We only travel once or twice a year so the max we can save is $20 a trip maximum. If we only hit toll roads back and forth to the airport, we would only save $8.
While this new Visitor SunPass has no cost, if you forget to return the visitor pass, you are charged $10, and the older transferable SunPass cost $25. Also you have to go online and register the rental car before using it so you really have to do this before you start driving.
I appreciate these alternatives as they forced the rental car agencies to be more competitive.
Ironically, for us, they have driven the costs down so far that we just use the rental car transponder as we don't have to worry about registering and unregistering the vehicle and we don't have to setup an account and give our credit card number to get the pass. As far as dealing with stray incorrect charges, you can still have that with any rental with a transponder in it....
Not to diminish the new pass but you really have to look all alternatives and see which fits your trip plans better.