It gives a nice crisp image in the center, the edges are a bit blurry, but that's to be expected from a lens for a phone...
It doesn't really work with a case at all though, I have an iPhone 6s Plus and even with the extra thin case I have on the phone it produces incredibly blurry images all round, the lens has to sit pretty much directly on top of the protruding iPhone lens. It's ok if you go without a case though!