This small, bright LED is so well thought out that it's a wonder no-one had thought of it before. The unit simply clips into the helmet strap and sits snugly around the temple area of a modern helmet. Compatibility with three different brands seemed good (although a challenge on helmets with an integral sweat/insect net).
Rubberised on/off switch is precise and nice to use, although a little tricky with gloves. The two white LEDs produce a surprising amount of light, particularly in flashing mode and their positioning on the helmet offers welcome additional security when crossing roundabouts, turning into roads or stopped at a junction. A bit concerned that it might become detached on rougher surfaces I wore it on a long bridle path ride and was pleased to find it still firmly in place on my return. For all its virtues, it should only be seen as supplementary to good lighting and given the falling price of LED lights isn't particularly cheap. However, it is well designed and is also available in red for rear visibility- can you ever be too well lit?