Our first trip to WDW in 2012 included my mother who has health issues. I rented her an
ECV using someone offsite, I don't remember the name. I will list the pros and cons. Just keep in mind that despite the cons I would not have changed my decision to rent the ECV as it allowed her to enjoy the parks with myself and my daughter.
First the pros:
The batteries are removable so you can keep the scooter in your vehicle. We would just bring the batteries inside and charge them overnight.
The seat was comfortable
CMs would give you front row seating because you were in an ECV

Great spot for the little ones to ride with Grammie when they got tired. (My daughter was 8 and she loved it)
Cons:
Removing the seat to fold the scooter can be hard! There were times I had to find a strong man to help me (and I pride myself on my independence).
Lifting the scooter into a vehicle can be done on your own, but it is awkward and heavy. After a full day of walking lifting that darn thing was well, something I can't say on DisBoards

I needed to upgrade my rental vehicle to a SUV and made sure the back/trunk area was flat. Some of them had a recessed trunk that made lifting the scooter in/out very difficult
ECVs don't stop on a dime and people WILL walk in front of you. This drove my mom crazy that people did this, plus she was terrified if a child ran in front of her. Keep in mind that the ECV wouldnt badly hurt someone, but it would still hurt a bit
Reversing can be .... interesting. (Maybe that was more of a mom issue than the ECV!)
The 'Is what it is':
CMs will move the ECV to the 'stroller' parking areas. Don't panic!
You will be asked to hold everything! Gotta love the front basket



A plastic bag to cover the batteries and steering controls is provided in case of rain
In conclusion if I had to do it all over I would still have reserved the ECV for my mom. There is no way I wanted to push a wheelchair or have her try and wheel herself while in a hot and tiring theme park. Plus, my daughter got some awesome Grammie snuggles

The ECV allowed us to enjoy Disney together as a family.