Did some testing with Mini LF and Amira/Mini EF mount. Both with cine lenses and EF still glass. Definitely vignetting issues depending on focal length, iris setting and focus. Master Grips work with internal lens motors (tested Canon EF L and Sigma Art), IS worked as well, but when camera is turned off and back on the iris setting defaults to high value - almost or completely closed iris which is a bit annoying.
As for as the vignetting issues: It seems to be necessary just to "shave off " a bit of material inside the mount? Is this something that's being worked on at Arri?