Not necessarily a con, but it has either one or two modes, depending on the model.
if you are seeking a tactical light then the mode selection is not a problem.
For comparison, I have a single mode Solarforce L2T, that I use as a tactical light. (solarforce is a inexpensive, quality Surefire clone). The Solarforce lights are sold as a host light, then you add the LED. I have a model L2T, with a single mode XM-L that outputs about 600 lumens. The L2T can run on CR123 or 18650 batteries. The cost of the Solarforce L2T and single mode XM-L was less than the cost if the G2X.