Recently bought an A7Sii and also looking to invest in glass.
I borrowed a friends EF lenses to get to grips with the camera. Mainly used the 50mm Canon f1.4 attached via Metabones IV adaptor. I'm very happy with the image from the camera. Especially shooting S-log 4K. However I have found a few niggles.
1 - Sometimes I switch on the camera to shoot video and the screen stays black. Switching off and on does tend to fix it.
2 - Sometimes whilst shooting the camera suddenly stops recording and does a weird fast over exposure.
3 - Sometimes once I've set my exposure for a certain environment and switch the camera on after a while it shows as being very under exposed. Switch off and on again often sorts it and reverts back to the well exposed image.
From a bit of research I am thinking it may be the metabones not translating everything perfectly all of the time. Don't get me wrong this is workable as it is, but quite frustrating especially when you need to get recording straight away to catch some action.
I think I need to update the firmware on the metabones. Unfortunately had to give the lenses back so thinking of getting the cheap(£70-100 second hand) Canon 50mm to test more. But I am planning to go in to a Sony store with my camera and do some testing to see if the Sony lenses fix all of these issues.
I'd be interested to see if anyone else has had these issues. Maybe I'm missing something.
Also if anyone has the perfect handheld rig that'd be good to hear about.
Hope this helps.