On our recent trip over Christmas, we rented from Gold Mobility and had a great experience.
Delivery - they delivered to our hotel (Surfside), but they do not deliver to Aventura and one other, Portofino maybe? They actually delivered a day early, not sure if that was because it was a busy time or not.
Scooter - the scooter was in great condition, felt brand new. The battery lasted all day - one day, we rope dropped early entry and stayed in the parks until close. We only lost 1 or 2 bars on the battery gauge (out of 10 or so). The running lights were nice at night helping others to see the scooter. It was easy to disassemble, load into our Highlander, and reassemble as needed (loading in the car is doable for 1 person, but much easier with a second person helping).
I don't think we saw any other Gold Mobility scooter while we were in the parks. That made it easy to find ours when we came out of a ride, store, or restaurant.
I think the only downside was that they price at a 7 day minimum and might be a little more expensive than some others we saw.
We'd absolutely look to rent from them if we needed a scooter again in the future.