The Basic licence for WooCommerce Product Add-Ons Ultimate entitles you to updates and support for 1 site.
The Pro licence entitles you to updates and support for unlimited sites, plus extra features like percentage-based pricing and group accordions and tabs, as well as additional fields like Calculations, Child Products, Checkbox Groups and Image Swatches.
You can see a full comparison table of the differences here. Click on the Basic v Pro tab.