Lots of people here use rental scooters! You have come to the right place to get your questions answered!
Actually, most scooters can be disassembled; it comes down to how heavy the parts are, how many parts there are once it's all apart, and how difficult it is to take apart/put together.
Here's a few things to consider:
The bigger and heavier the
scooter is, typically the better the ride. I say "typically" because there are, of course, exceptions to every rule. And the #1 rule you HAVE to follow about scooters at WDW is their size: They must be able to fit into a box that is 30" wide by 48" long. So, you can't rent a ground-pounding Super Scooter that holds four adults and expect to get in anywhere at WDW. (And that's the other big rule - one seat on the scooter, one rider only. No holding kiddos, no lap babies, etc.) Plus, you have to be able to get it into your room every night so that you can charge it overnight.
Super lightweight, easy to manage scooters do exist - and some of them are quite comfortable. However, when you rent a scooter, make sure that you take into account *why* the driver needs assistance. If they have knee issues, then a four wheel scooter with a flat floor that is easier to get on and off might be appropriate, whereas if they have back issues, a scooter with a higher seat back might be better. Let your rental vendor know *why* you need a scooter - and if they ask, be honest about your height and weight - so they can match you to the scooter that will be best for your needs. They deal with scooters all day long, they truly are the experts.
If you are considering driving to and from the Parks because of the scooter, don't worry - it doesn't take more than one or trip bus trips to get the hang of loading and unloading the scooter, and the drivers are always ready to help, especially if you let them know you are a new
ECV driver! I know that a lot of people just don't like the buses in general - if that's the case, then be prepared to take the scooter apart and put it back together every. single. time. you. want. to. go. somewhere. Those buses start to look attractive really fast!
Regardless, be sure to take 10 or 15 minutes at your Resort to get used to your rental scooter. Drive it up and down "curb cuts", through the gift shop, practice backing it up, making tight u-turns, and most importantly - practice panic stops or emergency braking, so you know how long it takes to stop. Taking those few minutes to get familiar with the rental will help you feel much more confident.
I own my own scooter - it's super lightweight, folds down easily, stores easily in a case the size of a golf bag, fits perfectly in the back of my Kia Soul... and I never hesitate to take the buses at WDW with it. (And no, you can't rent this model in Orlando. Sorry.) I'm on vacation when I'm at WDW, and the last thing I want to do is load and unload my scooter eleventy-hundred times a day. I prefer to let Disney do the driving; I just drive on and off the buses (and boats and Monorail) and get on with having fun!