Review The silence at the end of the phone was unusually ominous. “We've got something for you,” said the voice from Vulture Central. “Great - what is it?” Silence, then: “Just open the box when it arrives...”

Twenty-four hours later and a small black 300g rugby ball shaped dancing MP3 player is sitting on our desk:

From a design perspective, Sony's Rolly is actually a rather cunningly constructed little box of tricks. The speakers sit at each end of the device covered by 'ear' flaps that can open at up to 90°. These flaps are in turn mounted on end caps that can rotate through 360°.

Inboard of the end caps are rubber rims that rotate in either direction giving the Rolly the ability to move forward or backward or spin on its axis. LEDs run the diameter of the device at the junction of the end caps and the rims while another set of LEDs surround the function button.

All those flaps, hinges, rims and lights allow the Rolly to execute an impressive array of moves and pyrotechnics - 700 individual lighting effects, according to Sony - while keeping everything remarkably compact.

The design does, however, have one major flaw. Every time the ear flaps close during a dance move, the sounds falls into the toilet because they cover the speakers. This is shame because with the flaps open the Rolly produces a very nice sound for something its size, with solid bass, focused treble and no distortion whatsoever, even at higher volume levels.

The Rolly's exterior controls are limited to an on/off/Bluetooth slider and a well-concealed mini USB port. Changing albums and tracks is achieved by rolling the device forward or back. Spinning the unit on its axis, either clockwise or anti-clockwise, adjusts the volume.

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There is also a shake-to-shuffle mode, but be warned, the Rolly isn't the ideal shape to hold when shaking. Cue Wii-style $5m lawsuits?

The device comes with a Windows-only application called Rolly Choreographer which allows you to transfer MP3 and AAC files to the device and create custom dance routines. In the interests of science, we also dropped a track directly onto the Rolly using an Acer Aspire One netbook and it promptly shimmied its way through the song with nary a pause, so Mac and Linux users aren't completely left out in the rain.

At this point, it would have given us certain satisfaction to report that the Rolly is a hopeless waste of money and plastic, but to be honest watching it can be curiously hypnotic, especially when the choreography was been well planned.

Our review device came with three pre-loaded tracks, including the Foo Fighter's song The Pretender. The dance routine for this was frankly superb, the Rolly twitching, jiggling, flashing and spinning like a Dervish on speed.

Left to its own devices, the Rolly's dancing is a little less impressive and highly dependent on the music. Propaganda's album Secret Wish produced some nice moves – down to the exaggerated stereo effects and interesting harmony lines, we would guess, while Mozart's Requiem resulted in the gadget just sort of sitting there and flapping a bit.

More surprisingly, the automatic dance routine for Katy Perry's Hot'n'Cold was very subdued, suggesting it takes more than a simple beat to get the Rolly's creative juices flowing.

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As shown by The Pretender, the truly impressive effects are to be had by creating your own routines, but they're not half complex and time consuming things to set up, if our efforts were anything to go by. Luckily, the Choreographer software includes a 3D Rolly animation so you can get an idea of how your moves will look without having to load them onto the Rolly and try them out for real.

Apart from being more visually impressive, manual routines can be arranged to keep the ear flaps open which makes things sound better too.

If you can't be bothered to design your own routines fear not, dance 'move' files can be downloaded from – and uploaded to – the Sony web site and imported onto you Rolly.

Sony doubtless hope that there is a whole community of programmers out there burning the midnight oil in single-minded pursuit of the Rolly groove.

To avoid it running riot and terrifying the neighbours, the Rolly needs to be re-set to dance mode at the end of each track or after seven minutes of continuous motion.

On an altogether more mundane level, the Rolly can also be pressed into service as a Bluetooth remote speaker. It works perfectly well in this role but you have to forgo the dancing and strobe show – it just sits on your desk pumping out your tunes and looking a little apologetic.

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Sony's efforts to give the Rolly usable navigation and indeed a use, does rather beg the question why it didn't go the whole nine yards and fit a small screen and headphones jack when there certainly seems to be the space.

Since the Rolly has no method of detecting table edges, get it too excited and it will boogie straight over the edge and into oblivion. Thankfully, Sony includes instructions to re-attach the ears and drive rims should it not survive the drop intact.

Americans can buy an optional desk charger for $50 but we Brits have to make do with charging through a USB cable though we do get a plastic stand to stop it rolling around the desk. A full charge will see the Rolly bop until dawn, so long as dawn is not more than five hours away.

Now, £240 for a device devoid of any real function makes any discussion of value for money a little pointless though it's hard to ignore the little voice that says that if you want to spend that sort of money with Sony you could by an eBook reader and an MP3 player and still have a few quid in change.

Verdict

Playing with the Rolly is a bit like indulging in a quick spot of hand-relief when you should be working. You know it's a waste of time, you know it's wrong and you know you may very well go to to Hell for enjoying it, but that doesn't stop it being moderately amusing.

But how do we rate something with no tangible use? Right up to 90%, because it's the best dancing MP3 player on the market? Or just ten per cent, because it answers a question nobody was ever going to ask?

We'll give it 55%, because the sound is rather good when the ear flaps are open and some of the dance moves are impressive. And it may be the basis of an entire sub-culture that we are just too old and serious to really understand - like Pokémon or David Cameron.

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