They're known variously as "hoverboards" or "rideables" and are the latest must-have at the feet of celebrities - but the Crown Prosecution Service says riding them on public UK roads is illegal. What is this futuristic new breed of transportation - and how practical is it?
Within five minutes, the teenagers begin to circle.
They are drawn, camera phone first, by the contraption at my feet.
Trying desperately not to wobble, I'm attempting to look casual - difficult when you're wearing head-to-toe safety gear.
"These are so trending online right now," one boy says, as he films me helplessly spurt forwards and spin in a circle.
"What's it called?" asks a girl, as I unintentionally meander backwards.
Actually, it's a good question.
As yet, there's no real consensus on a name for this new genre of gadget, which counts pop singers Lily Allen and Justin Bieber as well as footballer David Beckham's son Brooklyn among its devotees.Image copyrightRex Features; GettyImage caption
Some call them "self-balancing scooters" or "personal transportation devices". Others refer more concisely to "rideables" or - with a nod to Back to the Future II - "hoverboards", despite the fact that, clearly, they don't hover..
But despite becoming a relatively common sight on the streets of the UK's main cities, "self-balancing scooters" are actually banned under section 72 of the Highway Act 1835 for use on public pavements and roads in the UK. The Crown Prosecution Service has issued guidance stating they "are not legal for road use".
According to the Department for Transport, the only place where it is legal is on private property, with the owner's consent. The same applies to Segway scooters, with one Yorkshire man successfully prosecuted and fined £75 for riding one on the pavement.
They come in all shapes and sizes. A large hands-free variation of a transporter ridden by a cameraman sent sprinter Usain Bolt tumbling at the World Athletics Championships.Media captionBolt wiped out by cameraman
The one I am trying - on private property, in order to stay within the law - looks like a cross between a forwards-facing skateboard and a Segway scooter, but other designs resemble motorised skateboards or unicycles.
It works by using gyroscopes to counter-balance and control the speed of the wheels. The more you lean, the faster you go. Twist your feet to turn. Lean back to brake.
Dozens of brands have sprung up, some even equipped with blue under-lights, music players and bluetooth. Hovertrax, Phunkee Duck and IO Hawk are among the better known US makes. Over the last year, brands have also started up in the UK, including Jetboard, Megaboard, Airboard and Legway.Image copyrightAPImage caption
Despite all this, it would require Parliament to change the law for riding one on a public street to become legal.
Former Liberal Democrat MP Lembit Opik - who campaigned against the ban by leading a protest convoy of Segways to parliament in 2008 - said it was "ridiculous and irrational" that a 200-year-old law was being used to prevent people using personal transporters.
"It's insane, because any common sense says they are very eco-friendly and a sensible alternative to public transport and cars," he says.
"These things aren't going to kill people. All of them should be allowed on the pavement, because people aren't stupid, they will get out of the way if they see one coming."
He said he regularly uses his Segway on roads and in cycle lanes around Westminster and has never been stopped by police.
But even indoors or on private property where personal transporters can be legally ridden, users would be wise to check the rules.
American rapper Wiz Khalifa claimed on Twitter that he was handcuffed by customs and border patrol officers at LAX airport because he refused to disembark from his transporter.
"I stand for our generation and our generation is gonna be riding hoverboards," he wrote, adding that he thought the officers would probably be riding them soon as well.
Bank cashier Jessica Williams, 23, from south London, who bought a Megaboard two months ago, agrees - and says there are far more uses for the contraption than she originally thought.
"I think it exercises your muscles, so I use it to work out. I play with my niece on it. You can dance with it - I've taken it to a club. I've ridden it in 4in heels," she says.
"Obviously you get a lot of attention, but I don't mind the attention."Image caption
The boards certainly caused a sensation when they first appeared at technology fairs at the beginning of this year, says technology journalist Olly Mann - but he doesn't think the buzz is likely to last.
"Most new innovations now are apps or things for your phone, so it had everyone talking - here was a cool new gadget like something out of The Fifth Element," he says.
"But I think the novelty will be short lived. There's probably a long way to go before its peak - at the moment it's mainly a lot of hipsters riding around and crashing into each other. The sweet point is when it's £200 and in Toys R Us for Christmas."
Despite appearing to defy physics, the type of device I'm using is fairly easy to learn. After a wobbly start, 20 minutes of practice should have most people rolling around with confidence.
Top speeds are billed at between about five and about 12 miles per hour, depending on the brand. Travelling with your feet so close to the ground and no handle bars, that certainly feels fast.
There are limitations though - steep slopes, uneven ground, and crowds are all difficult to negotiate. Puddles are not advisable.
At 10kg (22lb) it's a hefty weight to carry, and it also comes with a hefty price tag of between £300 and £1,200, depending on the type of transporter.
But once you get the hang of it - and overcome the embarrassment of being stared at - they are undeniably great fun.Image copyrightALAMYImage caption
Back at the spot where I am attempting to master the art, the gaggle of teenagers have not yet lost interest - and actually, it's not just the younger generation that are curious.
Seventy-three-year-old Philip Brannon from Croydon, who describes himself as an "active retired person", stops to watch the flailing Swan Lake I'm performing.
"I'm sure there will be lots of people over 65 who would like to have a go - as long as there's someone to hold them. I think it would be great for getting around supermarkets," he says.
Not everyone is so taken with the idea, though. Commuter Joel Harrison from Windsor, who hasn't seen anything like it before, stops for a look, but decides he would be put off by both the price and the weight.
"And it's quite a lazy contraption, by the look of it."
As for me, after several days I actually feel fitter - perhaps from lugging the board between places where I am legally allowed to use it.
And I have lost the wobble, if not quite the self-consciousness.
But when the time comes to return the board to the manufacturer it's quite a relief.
I think two legs are still better than two wheels.Image copyrightThinkstock
Skateboarding is a big deal on the streets of Tacoma, Washington, these days - but only a few years ago it was banned by the authorities.
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