I've found that the more useful such a vehicle is relative to speed and range, the less useful it is relative to size and weight. I've tried a Boosted Board, a One Wheel, and spent some time on my hangar neighbor's unicycle (In Motion). Sufficiently portable, but potentially dangerous, and the older you get, the greater the consequences of lunching the thing on a crack or rock that you wouldn't' even notice on a bicycle.
I gave up on convenience and have had a Segway Ninebot scooter for a few years. It's fast, easy to ride, and has a 28 mile range...as transportation it's great. But it's big and heavy. If folds up, but even so, getting it into the back of an RV is quite the exercise, and it think would be impossible without a SuperTrax canopy extension. These days, I mostly use the thing to zip around the airport visiting friends and getting to the bathroom (which seems to be getting farther away every year). Probably, there's a better compromise scooter out there than the one I have, but unless my mission changes I'm sticking with this Ninebot.