Or you should say buy 5 spare batteries over a multifunction hand grip comparing $ for $.
So the multifunction handgrip allows you to recharge your battery from AC and download your photos w/o taking off your base plate on top of GPS function not to mention a flash ISO/DIX PC syn port and a full flash SCA port when the hotshot is taken up by EVF2.
Although I have a spare battery but I prefer to charge my camera through a power supply cord when I travel, saves me the trouble of swapping batteries that often.