If you are going to rent a ECV, you might want to rent one from off site. They will cost less and you will have it all the time, not just in the parks. Also the parks have a limited number of ECV's to rent, and they are on a first come/ first served basis, so you run into the possibility of none being available to you when you need it. You also can not take it from one park to another.
Apple Scooters is a good company with some of the lowest rates out there for their ECV's.
Thanks again, peemag!
My aunt had an unexpected foot injury before her trip a few weeks ago and went with Apple. She was impressed and they were a lot cheaper!