What is the difference between BrandingUI and PrintUI Pro?

Simply put, BrandingUI is designed for users would don't want or need integration into their website.

BrandingUI provides a simple interface for making templates available for online editing as well as a basic workflow and notification system. BrandingUI does not offer access to our APIs which are necessary to do custom integration.

PrintUI Pro is pretty much what you would call a black box. You need to use some kind of integration into a system of some kind. The system can be a shopping cart such as Magento, or a full workflow system such as the ones provided by our partners. It can even be a customized system developed by you. If you need an online shopping cart, make sure you check out our Magento quick start kit as well as our ready-to-go Magento web to print storefront theme.

To sum up, BrandingUI makes it very easy to get up and running with no programming or HTML skills, but has no integration capabilities outside what is offered as part of the BrandingUI package. PrintUI Pro offers full integration capabilities with a more complex process required to get started.