Single or double batteries for my Sanwu Challenger II 520nm 1W laser pointer?

I'm looking at getting a Sanwu Challenger II 520nm (green) 1W laser with a G7 lens and an X3 Beam Expander (see here). The battery configuration options are either a single 18650 battery or else two 18350 batteries. The single 18650 is $10 while the two 18350's are $14. My initial thought was to get the single 18650 setup - less pieces to keep track of, and cheaper. However, I wonder if either setup will affect the overall size of the laser pointer..

Other than the price difference, can anyone tell me any advantages/disadvantages to getting one style of battery configuration over the other?

Thanks for your advice.