The SunPass works well on Florida toll roads, in that you purchase the pass and attach it to you windshield. You load the pass with funds before traveling on the toll roads. You are billed at the rate posted.
Problems arise in South Florida. Somewhere near Miami toll booths booths disappear. If you have a SunPass you are generally in good shape. Without one it is hard to avoid the toll by tags roads. they even have lanes designated as toll by tag lanes. It is easy, without knowing it, to end up on one of these roads, especially around Miami International Airport.
Unfortunately, somehow I ended up on one while taking someone to the airport. The total bill was about $15.00 for a $2.50 toll (handling charges added by the state).
It was after this experience that I purchased a SunPass.
I love this “tag number” business. Far as I know, tags go on clothing and license plates go on cars.