I was able to get my hands on a Sigma MC-11 Mount Converter at WPPI 2016 in Las Vegas which at the time of these tests was loaded pre-release firmware that at the time of testing only supported the Sigma 50mm F1.4 DG HSM Art and Sigma 18-35mm F1.8 DC HSM APS-C Art Lenses.
When tested with Sony a7RII and each of these lenses, the MC-11 adapter offered fast and accurate PDAF and provided full AF functions for stills including focus tracking and Eye-AF. I did not test video AF.
However, and I want to stress this was PRE-RELEASE FIRMWARE, the MC-11 that I tested was unusable with any of the other supported lenses on the list. The viewfinder either went very dark (as in nearly black) when tested with the Sigma Art 150-600mm F5.6-6.3 EF mount and totally blown out (nearly white) when tested with Sigma Art 35mm F 1.4 EF mount.
Sigma reps told me that the final release firmware for MC-11 will support all 15 Sigma Art, Contemporary and Sport lenses listed below when the adapter is released.
There is an USB port in the adapter that allows users update MC-11 when future Sigma Art, Contemporary or Sport lenses are released. Just don’t hold your breath for support of older Sigma lenses or Canon glass.
Sigma’s list of Sigma EF and SA lenses supported on MC-11:
Sigma 24-35mm F2 DG HSM Art Lens
Sigma 24-105mm F4 DG OS HSM Art Lens
Sigma 120-300mm F2.8 DG OS HSM Sports Lens
Sigma 150-600mm F5-6.3 DG OS HSM Sports Lens
Sigma 150-600mm F5-6.3 DG OS HSM Contemporary Lens
Sigma 20mm F1.4 DG HSM Art Lens
Sigma 24mm F1.4 DG HSM Art Lens
Sigma 35mm F1.4 DG HSM Art Lens
Sigma 50mm F1.4 DG HSM Art Lens
Sigma 17-70mm F2.8-4 DC MACRO OS HSM Contemporary Lens
Sigma 18-35mm F1.8 DC HSM Art Lens
Sigma 18-200mm F3.5-6.3 DC MACRO OS HSM Contemporary Lens
Sigma 18-300mm F3.5-6.3 DC MACRO OS HSM Contemporary Lens
Sigma 50-100mm F1.8 DC HSM Art Lens
Sigma 30mm F1.4 DC HSM Art Lens
Notes: MC-11 is not compatible with teleconverters.