Well..I think showing you a bad pic or good pic doesn't say anything about the flash. Unlike image quality of cameras or lenses, pics cannot show how a flash performs, it can only show how I use the flash.
Overall I think the build quality is pretty good. TTL is accurate but I shoot manual mostly anyway. At a relatively low price (around 350 for the combo) I think it's a good deal.
It's not a big investment anyway, if you dont like it, you can always sell it.
The most important point is, if you want to shoot off cam flash with TTL support using 2.4G radio trigger, the Nissin combo is pretty much the only choice for MI mount.
For cosplay events I don't use flash anymore unless I can setup a booth (which I am too lazy to do, and I also need to enjoy the event myself....). Don't like to shoot in AFA anymore nowadays as the lighting is really bad and the convention is always crowded. Also the ceiling is to high for bouncing. I have tried on cam flash, off cam flash, all kinds of diffusers, it turned out that I simply cannot get good shots with or without flash. For outdoor events like EOY, flash is really not necessary, Sony cameras have enough DR to handle the highlight and shadow. It's just my two cents.
Here are some shots I took in C85 2013 with the original A7.
EOY 2014 with A7
This year's EOY with A7M2
last week's ICDS with A7R2