Not considered important by the manufacturer!

Despite the low price, I like the processing, very stable, nothing wobbles.
Sure, the autofocus is slower (guess about 2 to 4 seconds, depending on the lens) - but I use on my A7s anyway prefer manual focus.
So far I could 17-40mm 4.0L, 2.0L 135mm test and the 35mm 1.4L - here the AF works as I said, but just very slowly. For however accurate - if the AF is "ready" to fit well.
BUT:
I have annoying reflections in the photos that are too large area partly to rid it with Photoshop. This happens when a bright light source at the edge or just outside the visible area of ​​your lens is.
To counter I bought with velor and line the interior of the adapter. Had I not done would be the adapter again gone back there gets very easy to use in night shots and difficult in daylight only in "good conditions".

In summary:
Adapters "out of the box": 3 stars
Adapter with velor foil inside: 5 stars (because the price is still far cheaper than the latest Metabones model, which is padded with velvet.