Designed as 'sports' lights for cycling, jogging, rollerblading and so on, these are unusually powerful for their size. At only 5x3cm and a handful of grams, they will still get you noticed, to say the least, despite their only having a single LED.
While the front LED doesn't emit enough light for off-road riding on a regular basis, you can still get some illumination from pointing it right down in front of you, so that it would serve as a get me home' off-road light; undoubtedly though, the main use is for riding on lit roads. There was nothing evident on the packing or the lights themselves suggesting they conform to the relevant BS standards, but in practice you are unlikely to ever get stopped using them because they have quite a high dazzle factor (due to "advanced optics", says the Sigma blurb).
Two sizes of velcro strapping mean they will mount just about anywhere on your bike or about your person (though strapped around a jacket arm they could easily be obscured by even small folds in the material). The claimed battery life is 30 hours and our lights are still going strong after about 20. Batteries are the small, circular 3V lithium coin' cells (CR2032 - the most popular size of this kind), so obtaining and carrying spares is a doddle. The only annoyances were the fact that the underneath of the lights were a little slippy for bar mounting and the velcro a little long for some smaller bars - niggles easily sorted with a strip of rubber.