From an electrical engineering point of view, it's terrifying. Pretty, yes I grant you. But potentially very very dangerous.
Well, the most obvious one (to me) is the risk of mixing up the life and neutral wires by twisting the plug the wrong way. The fuse is also accessible during use, which is not recommended.
If you want the appliance to work, no. If you don't want to get killed, yes. The live one is the one that goes through the fuse, and the neutral one is the one that's grounded. You don't want to mix them up.
And in any case it should be simple to only allow it to rotate in one direction.
It *should*, but you have to think about failure modes. What if that protective bit of plastic snapped off? What if the one-way mechanism broke? Like I said above, the danger if you mix them up is high, so you would need a completely fool-proof system that would never go wrong, and mechanical things rarely fall into that category.
Thanks for giving me solid reasons to beat up people who link to this thing in the future. I'm fed up of the "Oh, why are British plugs so big?" commenters, who don't realise the AWESUM POWA of our 240V AC, with its 13A 3kW kettles, able to make us cups of necessary refreshing tea in mere seconds, delivered safely (and cheaply) due to the wonder of the BS 1363 plug.

That's on top of the fact this is a prototype, which barely exists outside of videos and plastic mockups. Call me back when it's passed said British Standards testing and is in mass (hell, even limited) production.
Does saying "this is cool" really warrant that level of grumpy? In any case it's hard to believe modern circuit breakers have the same requirement for appliance connections as fuse wires of the 50s did, so *is* the BS1363 really still necessary?
Oh, if it was just you I wouldn't have bothered, but this has been doing the rounds since the middle of the summer and everyone seems to go crazy for it, while laying in to the standard plug. (I was going to apologise in advance for the grump, but I figured people knew me. Also, seeing the same link is my problem for being online way too much, not yours.)

As to the comment about modern circuits, I'm pretty sure British wiring still uses the post-war ring main paradigm, so you do need a beefy per-appliance fuse. Sure, that might be less true for, say, iPod chargers, and yes, the USB conversion trick is a nice bit of design, but for things that actually have motors, I still approve of the earthed, fused plug.
Indeed, given the number of DC, non-earthed devices out there perhaps there is a limited utility for such a connection. That said, perhaps USB is already it.