One of the things I love about Fuji cameras is the small size. But the smaller size and packing the back with buttons can sometimes be unwieldy for those with large hands. I use Lensmate thumb grips on all my Fujis--XP, XT, XE. Improves handling significantly without adding bulk. Gives the thumb a place to rest without pressing buttons inadvertently. Works for me but others may prefer fuller hand grips.
One note--I've used cheap generic model thumb grips before settling on Lensmate models. I personally like the Lensmate better and I can justify its higher price. Never tried any of the other higher priced brands.
I cant speak for the Fuji specifically but on my Leica M8 I use both a half case and a thumbs up. I find they each have a place in stabilizing my hold on the camera. And yes it pimps the camera too. The camera came with both the standard base and a base with inbuilt grip. I used the latter for a while but found that I liked the extra grippiness conferred by the half cases leather over the extra hold conferred by the hand grip. In general I think all small form cameras benefit from some kind of help in this department. I have owned and used Olympus, Sony and Panasonic cameras (all except Fuji on fact :^) )and it applies to all of them. Of course DSLRs tend to be different due to their larger size and the fact that these days they usually come with a large hand grip inbuilt.