I think this is a must for cyclists, I have never felt particularly safe with my standard, 'legally required' front and rear lights because I don't think they give enough visibility for vehicles. I've also found that to be the case when I'm driving and see cyclists just with the bog standard lights; it just isn't enough.
I was really suprised at how thin and compact it is, I was expecting something as thick as your average bike pump. This is really easy to put on and equally as easy to take off although the instructions are a bit ropey, but it's pretty self explanatory if you just get familiar with the attachment slings and the light itself. There's also the added bonus of being able to attach it to your jacket/top if you have a back pocket on it; which therefore lights up YOU rather than just the bike so it would also be great for joggers or walkers.
I've noticed cars do tend to drive past me leaving a lot more space than they normally would do and are therefore more cautious, so obviously it sends the right message to drivers, it makes for a much less 'hairy' ride in a city centre.
It's definitely brighter than an average rear light, it's light so won't add any extra weight or bulk to your bike, it's flexible, but I haven't worked out why I'd need it to be flexible yet!
It's compact and doesn't hinder your cycling, wherever you might decide to put it on the bike,(no rubbing against your leg), it also seems it's also going to be very robust, the rubber covering the batteries on the top and bottom would prevent the light 'filament' from breaking.
I hope they make, or intend to make a front light version, because I think these are fab.
I inted to get at least two more.