Christopher R.wrote a review of Blackburn Mars 4.0 Rear Light on May 13, 2009
Love the light. Rain and wind haven't yet managed to compromise the water-proof light housing, and I love the portability. It comes off when I park, or when I need it to clip to my bags and walk to work in the rain.
I feel safer with the 4.0, which is key.
Side-facing LEDs are a bit of a novelty, not very visible, and somewhat dwarfed by the 1W in the main face.
Highly compatible with any mounting solution--bolted right onto my rear rack, no problem.
One thing: stock batteries were basically shot, light output was 35% or so on receipt. Probably a floor model (It's a "test me!" package), and my silly fault for not swapping sooner.