Yeap a watt meter is very easy to use. You simply look at the display and compare the results to the max your equipment can handle.

Yes a balancer is worth every penny. I use the Astro Flight blinky. It's only $25 and work great. Using a balancer your batteries will last longer(more cycles) and be more consistent through out their useful life. The biggest issue with batteries is that the cells become out of balance and 1 cell can be over charged and another under charged. This will result in less available power and possinbly damage a cell.

Make sure batteries have a balance lead on them. If not a balancer would be a waste of money.