I rented last year and will again at the end of the month for my sister who will be 6 for this trip. I don't like her umbrella stroller because it is too low for me to push and Disney is the only place she uses one. Plus, travelling alone it was one last piece of luggage/equipment I had to lug through the airport.
The strollers are in great condition. We had no problems with them. They were always clean, easy to push and easy to control. In fact I pushed while walking beside it last time (since it was only the two of us it was easier to talk that way) and could steer one-handed.
I know many people say that the downfall to rental is that you don't have it to get back to the bus or around the hotel, but that wasn't a problem for us. She was old enough that she didn't get exhausted by the end of the day. Plus, having ridden all day she was fine to walk to the bus stops and then back to the room.
If you have any other questions let me know.