Looking at both, the G56 is better engineered too. The MMC version is a bit of a faff to fit but it can be done without modification and spacers (eventually). After all, the factory manage it.
At one point Williams were advertising a
Garge56 (sic) for under £1300 on their website.
Maybe a Chinese copy 
They took two weeks to answer my emails so I gave up. (They have now corrected it) Better to deal direct with G56 I suspect.
