For reasons unknown, Takara's  release of Random Booster ACT2 also saw the addition of a uniquely heavy CWD with it. Normally CWDs metal components weigh roughly 15g. 

The metal CWD piece that comes with many ACT2 beys is a full two grams or so heavier, weighing in at around 17g alone, which is usually the weight of a regular CWD with most plastic components included!

Normally a CWDs metal component has a thickness of ~6.8mm. These especially heavy CWD molds have a thickness of ~7.3mm. Not only is the ACT2 CWD heavier, but also thicker.

This means that, technically, the CWD that comes with RBA2 releases is the absolute best possible CWD to have. The metal part adds 2g to any combo, which is ideal for Defense and not too shabby for Attack types either. If you are using a Stamina type, perhaps the regular 15g CWDs are better, but that is yet to be determined.

With all that said, the only way to tell the difference between the two versions is weighing them, measuring them, and marking them for future reference. Other than that, they are indistinguishable from each other, no other molding differences are apparent. 

Note: See the HMS Weight Comparison Doc page to view my fairly extensive CWD Weight Disk weigh-in. This should give you a much better understanding of the weight differences between RBA2 CWDs and others.