I think using your left to drop the mag is so much more efficient.
If you use your right hand, you need to let go of the pistol grip, swap the mags, grab the pistol grip, then remove your left hand to pull the charge handle (because the charge handle is on the left side.... something else I had to get used to). Seems like a lot of juggling around.
If you use your left hand, you can keep your right on the grip, keep focus on the target, swap mags and pull the charging handle with your left.
Give it a try... practice both with either hand to figure out what works best for you. I still have a lot of practice before it becomes 2nd nature, as my background is with ARs, mini 14, etc, so I am used to swapping mags with my right then charging with the right too.