I had a Blackburn Mars and it was pretty good, until it fell off one morning because the temperature got to about minus five and plastic got brittle and couldn't withstand the vibration from the cobblestones. Evans wouldn't replace it without a receipt, and I never bothered sending it to Blackburn.
I've now ordered an S-Sun unit from CRC because they were selling them for about £4. If I were looking to spend a bit more I'd get a Smart 1/2 watt one, because at my most recent audax event loads of people had them.
I'm going to end up with a dynamo-powered SuperNova one in a couple of weeks, which is supposedly so bright it's illegal in Germany!