If you're working with a variety of Canon EF Auto Focus lenses with your Sony A7s, Sony A7sII or Sony A7RII cameras, you'll need a good lens adapter that can communicate to the lens so that you can at least change aperture values. Otherwise your lens will be stuck at one Aperture. At the same time, you'll probably need a variety of ND Filters to fit the different lenses - or at least a bunch of step up filters.
Or you can simplify your workflow and check out the new FotoDiox ND Throttle Fusion Adapter that has a built in Variable ND Filter (inside the lens adapter) while still allowing full communication to your Canon EF Auto Focus Lens and to adjust aperture settings from the camera's dials.
The FotoDiox ND Throttle Auto Lens Adapter is especially handy for people who love shooting in SLOG and wide open apertures. As the base ISO with SLOG on an A7s is 3200 (or 1600 on A7sII) normally your way overexposed. Adding an ND Filter as part of your Sony shooting kit is going to really help you control that SLOG exposure while keeping your super shallow DOF look.
Of course there are times when you need every bit of light you can get, so I can't say it's going to be the only Lens Adapters in your bag. Once you have this ND Throttle mounted you'll get a bit of light loss even at it's minimum setting ND. But I generally like shooting 'with' light and always try to add creative lighting to our scenes, so I could say this would probably tackle more than 80% of what we shoot with the Sony A7sII. It's definitely an adapter I think i'll use more over my Metabones.