They rent even by the week which is the best rate.
Please note, the scooters are designed to go a certain speed. Most are in the 4 to 6 mph range. They are not a car. You have to get a bigger model which is less portable to get faster speeds. I believe Disney slows down their full size scooters; so, you don't get full capacity. Also, note there is a speed control of sorts on the scooters. They are usually identified as turtle to rabbit. Rabbit is faster. This can make a difference.
If you let up on the handle you affect the speed of the
scooter, too. We find them to go at a good speed if you are using them correctly. There can be problems with scooters, but then you should get a replacement and not give up on a scooter. I'll share a story. Our MIL who was 89 at the time would let up on the handle to scratch herself or play with her sun hat or rub her nose, etc. Well, the scooter would stop each time she did this. We had two scooters and she complained hers was not working right. We traded scooters and she had the same problems. It was driver related, not the scooter. We watched her after that and told her she's letting up on the handle too much. Eventually, she learned. If your dad is having trouble with whatever scooter you pick you should ride it as well for a short distance to make sure it's not driver related. Check the speed to make sure it hasn't moved down to turtle speed.
The smaller, more portable travel scooters are not as comfortable as the Disney scooters. They are more compact and don't have as much leg room. The seat cushion is poorer on the smaller models. We find it ok, but there is a difference. Without a lift for the car, etc. it will be difficult to get a full size model.
Remember, you are responsible for charging your own, rental scooter if it's not at the park with Disney. The smaller, portable scooters don't hold the same charge as the bigger ones. You need to charge it religiously each night. You should be okay for the day if you shut the scooter off when you are seeing a show, parade, fireworks, eating, etc. If you leave your scooter on all the time, you may run into issues with the battery. There are outlets in the Disney parks, if you run into a problem that way, but you have to have your battery charger with you. We carry it with us all the time.
We have a town car and the pride to go 4 wheeler fits just fine. We have used our back seat at times for some of the parts. We need to use a wheelchair at times depending on who we have with us; so, we need to get the wheelchair in the trunk and therefore we have used the back seat, too for the scooter. I feel it's better if two people help each other taking the scooter apart and putting it back together and in and out of the car.