Just one thing to keep in mind, if your
ECV breaks down while at the parks, you will have to get it to the front of the park and back to the room/car. If you rent from someone like Gold Mobility, they will come to you anywhere within the park if something does go wrong.
Personally, even if I did have a personal ECV, I would still speed the $250 for that peace of mind alone, as neither my wife nor I could physically push it out of the park. Given the cost of going to Disney World, it seems a small price to pay for the peace of mind to me. But everyone has to make their own decisions on what is best for them.