In reply to Stone Muppet:
The red light (which can be set to be on constantly ie not flashing) is useful if you want light but don't want to completly screw up your night vision eg you're doing night nav on a moon lit night and want to check the map; similiarly the green light can be used to see red contour lines which wouldn't be visible under the red light, although I find the green is too bright so cover it with a piece of green electrical tape to dim it.
I find the rear light gives me a (probably completely unjustified) sense of safety when staggering back to the campsite from the pub via a dark country lane.
To the OP: They're not perfect (changing batteries with cold hands or in gloves is a pain) but for the money they're very good.