Don't think that with the features offered, 25cm is too big for an emergency light thats 11oz and waterproof...........and no worries about batteries running out!!
IIRC, this is similar to a light which got a mention in Descent a few issues back, intended for aircraft survival kits and that sort of thing. The one in Descent, however, was rated as a bit of a dog....
Because of the great big magnet you wouldn't want it anywhere a compass. Or any sensitive electronics for that matter. If you buy one, don't leave it on top of your telly or next to your laptop for example.
Also I imagine it would be unpleasant carrying it in a tackle sack with the magnet knocking back and forth.