Look also at this review : http://www.iso72.de/metabones-sony-nex-smart-adapter-mark-iv-vs-mark-iii-sealed-comparsionreview/
All this doesn't sound very good...
I own and use a King adapter that basically does the same thing with A7R.
Quality is probably lesser but there is no reflection I can see.
This is useful since you have to be able to set the Aperture on the Canon lens.
With the Canon EF 16-35mm f/2.8L, the AF works (slowly but it works).
Some lens have some play though.
In general, I'm not found of the AF on A7R (I also own the Canon-Zeiss FE 55mm f/1.8 ).
I greatly prefer using old Canon FD lenses with manual focus.
They are smaller, lighter, more comfortable to focus, cheaper and, in general, of very good quality.
Main exception is the wide angle EF 16-35mm zoom for traveling :
it's mounted on the A7R body when I travel and it's very useful.
I just purchased a Canon EF 16-35 f/4.0L IS -for quality in the corner and IS- and have to compare both...
Could well be the ideal combo for traveling !