I carry a 2x AA light at work. It is a general purpose tool but would is a legitimate defensive tool for my situation. In its normal grip (left hand, bezel extending past pinky), it can be a striking tool. I would use it in the same manner as SN's instruction on reverse grip edged tools that he covers in EWO, ECQC, etc.
I like the 2x battery option for a number of reasons. Output, runtime, and length all lend themselves to a well rounded item worth carrying.