its totaly all about handling!, when i got my d300 out of the box i didnt like how it handled one little bit, 3 days later it had an mb d10 straped to the bottom and now i absolutly love it, but if youve never had one you dont miss it, i never had one on my d80 for about 6 months and then bought an mb d80 and again fell inlove with the camera all over again,
i persoannly wouldnt have a camera without it!.
only downside is size, but im not worried about that
ohand is it worth it?
yes.... every penny
but IF its just for extra battery time, keep a spare battery in your bag