The only difference between the two different models is the material of the extension itself. 


The aluminum versions have aluminum extension tubes, while the carbon versions have carbon fiber extension tubes. All of the quick-release hardware, handlebar clamps, and other parts are identical between the two versions. 


Functionally, the only difference between the materials is weight - the carbon fiber versions will weigh approximately 60-70 grams less than the aluminum versions. They also look cool because, well, they're carbon.