Kenny is the tops when it comes to cart rentals and most likely I will never rent from Disney again.
However, I will say this. Back in May (Memorial Day) our trip was less than Kenny's minimum (which is 5 days), so we did rent from Disney. That entire weekend was pretty much solid rain from the time we arrived till the time we left!!
On the day before we were due to leave, we packed everything up ready to pull out the next morning. Well since everything was packed up, we had no shelter from the rain, and just sitting in my tiny camper all night was not gonna be fun, sooooo we decided about 10pm that night that we would hit the road. We dropped the cart at the late night dropoff, ran in the office and finalized our bill and drove north for a couple of hours and got a hotel.
If we had been renting from Kenny that wouldn't have been possible, as we would not have asked him to come out and get the cart that late at night. (Although knowing Kenny, he might have suggested a place where we could leave it.)
So, I guess my situation above is about the only convenience a Disney cart would be.