Summary: Basically, you're spending money to make bad photos. Trust me, you can make bad photos with the equipment you already have. I suppose if you're a hipster, or you're just a really bad photographer, this will give you the excuse you need to pass off bad photography as "art", but for the rest of us, it's just a waste of money. Seems well constructed. It's just a flawed premise.
Summary: You heve to get you pictures in a high ISO or in a very bright day. It is very hard to see where it is focused. Lost virtually 80% of the pictures I took with it. But... some are actually good and the effect is interesting. For the price, I can say it's fair.
Summary: I have a canon 7d which is an aps-c format sensor. This causes the field of view to be cropped very closely to the portion of the lens's sweet spot with only a small portion of bokeh in the corners. Since the lens is a fixed focal length and f ratio there is not much you can do to change the size of the sweet spot. Moving the sweet spot towards the extremes of the field of view is somewhat helpful.