Best accessory I have added to my GH3 is the battery grip. With the neckstrap around my shoulder and using the viewfinder you can get very steady level shots... the grip does just that... gives you great grip and better balance. The GH3 was missing this weight and extra grip. Also the extra function button and controls are really useful. Oh yes and you can double battery time.
Get it. Worth it.
Get it. Worth it.