I was using my Nissin i40 yesterday and have to say it is superb!. The size is matched perfectly to the sony body and it functions really well. It took me a bit at first to get used to when bouncing as I wasnt used to having a flash on camera. I always used my speedlight off camera previously as it was just to big on the body for my taste (even on my DSLR). Im now getting more used to where I should be directing the flash for the most even spill of light from the bounce.
It seemed to result in cold WB shots a lot of the time initially even when using the flash WB setting but its easily sorted in post. This was mainly evident in my own living room but I have white walls and ceilings so that may have been the issue. I used it elsewhere and the WB seemed correct.
The thing I LOVE about it is the on flash FEC dial when using ETTL mode. It makes on the fly alterations so easy.
Only negative I found (and still not sure 100% if its an issue) is that due to the nature of ETTL there is a VERY slight delay between the pre-flash and the main flash. For adults this is fine but for my son who doesnt look at the camera for more than a split second normally it could be an issue, and by that I mean when I am at the ready to take a shot, I manage to get his attention and he looks at the camera, I click the button and the pre-flash fires and by the time the main flash fires and the exposure is taken he has looked away a bit. Having said all that I was still getting shots when I felt this had happened so it may not be that big of a deal - further testing is required.
Now this is no fault of the flash and is more of a consequence of using ETTL with young kids. This would happen with any flash using ettl.
For the price I would recommend this flash to anyone with a Sony body.