My wife has one and it worked GREAT on numerous cruises. The ship is very accommodating for scooters, electric wheelchairs and of course your normal push wheelchair. Airlines are accommodating as well and will go out of their way to ensure they get on the plane.
We were able to park the scooter in the cabin by turning the seat in order to get it through the door. Charging the battery was never an issue. My wife's battery would last all day, even when on an excursion.
I saw many people this last week that should not be pushing a wheelchair of their loved ones around the ship. After awhile I think the pusher needed the chair as much as the loved one.
While in the tender port of Grand Cayman, even the tenders accommodated scooters and chairs so you did not have to lift the love one out of their seat and just ride them on and off the tender. One draw back is excursions. Not many will accommodate scooters, but can do it for wheelchairs...But some of the tour operators have wheelchairs available so we parked the scooter on land then used the excursion operators wheelchair until we got back to the dock where she jumped back onto her scooter.
Scooters will definitely save on your backs and so much easier for the loved one.