Per 67's website:
INTEROPERABILITY BETWEEN THE MAGMOUNT G3 AND APPLE'S MAGSAFE
Owners of the Apple® MagSafe Charger can easily use the MagMount G3 with Apple cases, but it will require either
(A) the use of 2 x small steel plates (included in item # G23044) installed outside coil area
or
(B) the use a 3rd Party (non-Apple) case that have embedded metal plates outside the coil area.
Suggested 3rd party cases that 67 Designs’ staff use interchangeably with the MagMount G3™ (on the road and on the trails) and the Apple MagSafe Charger (only at the desktop!) are the Pitaka MagEz cases.