On my first ever visit to China, I saw a bunch of people riding these strange devices (the red one on the left in the picture below) that I had never seen before. Like a Segway, except with only one wheel and no awkward handle. They are like unicycles, except self-balancing using an electric motor. Here is a video of the first two days with this: https://www.youtube.com/watch?v=cuxNoCBn7x8 The clip begins with my first two hours of practice and concludes two days later when I was successfully going around short distances with it.

First impressions The order arrived in about a week. Unboxing while getting pieces of styrofoam all over the floor. Included: device, charger and training wheels. Training wheels? That was a bad sign, as I expected this might be easy enough not to require any help. Just turn it on and it will magically balance me, right?
This thing is surprisingly heavy, like carrying a box of bricks. Why would you ever need to carry it though? Although theoretically you could ride it anywhere, realistically you do end up carrying it down the stairs or next to a power socket to recharge it. You probably don't want to roll a dirty tire along your floor. According to the specs, the weight is 10kg (22 pounds).

After turning it on the principle was clear. If you imagine just having a wheel freely turning like on a unicycle, you would need to balance yourself from falling on your face. Additionally you would need to balance against tipping left or right. In an electric unicycle, when power is turned on the engine inside automatically prevents you from falling forwards or backwards. But you still have to balance left-right yourself, just like on a bicycle.

Learning how to ride it
I carried it downstairs, turned it on and balanced myself against a wall. First feeling: wow, this is impossible! I tried for maybe 20 minutes but could not go forward for even a second without falling. Which way is the front anyway? Went back inside to read more and learned that the controls (power button, charging plug, charge indicator) should be on your right. It seems like this would be one of the things where having someone instruct you would probably be extremely useful.

After about 2 hours of practice I was able to ride all the way across the parking lot with only about 50% chance of losing balance in the middle. It's like learning how to ride a bicycle, in that you want to go slow because you don't know how to balance yet, but you MUST go faster because you can't balance it from a standstill. You have to keep moving to keep your balance.
Learning to ride this is a lot of fun. I found myself looking forward to the next session. For a few days my usual coding - web surfing - coding - gaming - coding routine turned into coding - airwheeling - coding - airwheeling routine. As you learn you are constantly lifting the thing up and then straining your legs in riding attempts, so it feels like a workout.

How fast can you go?
The promised specs for the X3 version is 16km/h (10 miles / hour). When first practicing, I was more concerned about how I could go slower to avoid possibly planting my face in the asphalt. After getting used to it for a few days, I did find myself wanting to go faster. The device seems to have some self-enforced speed limit. If you try to lean forward to go faster, you can get a short spurt of speed but then it plays warning beeps and you can't go any faster.

After a few days I tried a 30 minute continuous ride. Balance was no longer a problem at all, but I found that the ride was straining to the calves, which are constantly pressing against the plastic. I had the same pain when learning to ice skate. It seems to have disappeared over time. Link: http://www.bemmu.com/airwheel-electric-unicycle-review