So the little Nissin, this is my second flash gun for my Fuji set-up, the first being the badly made Fuji EF-42 which was a rebranded Sunpack flash except it's a lot more money.
The little Nissin is a small little thing, with a decent recycle time, takes 4 AA batteries, has full TTL Fuji support. Ive used this flash at a few weddings and it works very well on the smaller body cameras in the Fuji line-up.
As you can see on the left hand side image, you have several settings for how you want the flash to behave - TTL, Manual, Auto etc.
The wheel dial is used to adjust you manual power output - all the way down to 1/256th power which is nice; you can also change the TTL flash exposure compensation on the right hand side of the dial.
On the top of the flash is a small bounce card - usefull for catch lights in eyes.
The build of the flash IMHO is much better than the Fuji EF-42.
I tend to use flash very sparingly at weddings, if I need to add more light I will always go for higher ISO, but for the disco and after show party of a wedding, the flash does make an appearance when dragging the shutter.
Until Fuji bring their EFX-500 to the market I believe this is the best TTL flash you can currently get for the Fuji system. Its not by any means perfect, the flash is quite noisy, I always think I'm going to break the battery door and the dials for the wheel dont light up, so if its dark and you have no light - you dont know what power you are on!
But these are only minor complaints, its not going to produce the power of a Nikon SP800 or whatever they have now, but it does work very well and is the best choice right now for Fuji peeps.