The difference is that ProBundles don't expose the code. If you need to explore the code, it's all there on https://HubConnect.to
To install a ProBundle:
Select Bundles from the main menu and click Import Zip in the upper right.
Select the Download from a URL tab, select This is a private pro installer bundle, and then paste in either the Server bundle URL or the Remote bundle URL above. Click Import and the result is:
You can then import again using the UniversalDriver URL or use Hubitat Package Manager for the Universal Drivers.