On principal, I don't like to use batteries if I can help it, and so I'd rather use a dynamo tail light w/ the lower wattage 2.4W lamp. I haven't personally found that there's a whole lot of difference in brightness between a 2.4 and a 3.0W headlamp. In fact my dimmest headlight is a 3.0W B&M Lumotech Oval plus running w/o a taillight off a Shimano hub generator. My 2.4W B&M Lumotech standard plus headlamp running w/ a taillight off a B&M bottle generator is brighter. I half suspect the Shimano hub may not be putting out full spec volts / amps, but I haven't tried to hook it up to a meter to test it yet.