I've got one which I've used for the past 2 years.
As a commuting light it's been excellent. I use it on the flashing mode, it has quite a wide lens and as a result throws the light well to make me seen on lit roads. Been happy with the battery burn time too, in that it hardly ever need charging (I have a 20 min each way commute). Even when the battery is low (there is a little red indicator which comes on at the side of the lens) it's still been bright.
I also used it for the Strathpuffer (and night training rides) back in 2008, so have some experience on unlit tracks, and would say it was only adequate for that kind of stuff.
If you can get one for a good price and don't need it for doing anything technical then I would definitely recommend it.