I have written about the Viltrox EF-FX1 before.
TL; DR - the EF-NEX IV performs pretty much the same way as the EF-FX1, is marginally better in some cases, and worse in other cases.
AF performance is by and large acceptable to mediocre, with two notable exceptions: the Canon 16-35mm f/4 L IS and 10-18mm f/4.5-5.6 IS STM will not AF. On the plus side, the A7 II actually manages to AF the Canon 180mm f/3.5L Macro, which the EF-FX1 was unable to. AF is quite slow and not very reliable however.
The EF-NEX IV also manages to report the focal length properly (which the EF-FX1 could not), and it can detect APS-C lenses and automatically crop (I was unable to get the "tunnel view" with the 10-18mm IS STM).
TL; DR - the EF-NEX IV performs pretty much the same way as the EF-FX1, is marginally better in some cases, and worse in other cases.
AF performance is by and large acceptable to mediocre, with two notable exceptions: the Canon 16-35mm f/4 L IS and 10-18mm f/4.5-5.6 IS STM will not AF. On the plus side, the A7 II actually manages to AF the Canon 180mm f/3.5L Macro, which the EF-FX1 was unable to. AF is quite slow and not very reliable however.
The EF-NEX IV also manages to report the focal length properly (which the EF-FX1 could not), and it can detect APS-C lenses and automatically crop (I was unable to get the "tunnel view" with the 10-18mm IS STM).