Hi reltor; i have one of the 6ex units in my 2c-3,123 cell light and it works great. these are made for 6d lights and that is 9 volts... 3-123 cells is 9 volts too, so it should be fine.... if i have it figure right it should be in the 4-4.5 hour range... i had a mag star 6 in it before and it had good throw and good light,,,but it only lasted about 50-60 min., so i think you get more light and more run time.
i have two of these set ups and the one i changed to the terralux 6ex is the night stand light. i will probably be getting another one for my hunting light....lots of light in small package... just my .02
ocharry