Sixt - Sixt Cape Town Diamond Upgrade?

I am planning to rent a car in Cape Town. Does anyone has experience how they handle Diamond upgrades.

Thx in advance

I'm planning to rent from Sixt in Cape Town next February and i'm a Platinum holder so am interested as well.

Sixt is in co-operation with a local car rental operation operating under the brand name "First Car Rental". I have never ever ever received an upgrade at CPT from First Car Rental. Granted, I am only Sixt platinum.