What a Rainlendar Pro license key is
Add a text field to directly paste a license string instead of requiring a file download/upload. Status Indicator:
High Customization: Supports extensive skinning and "mix-and-match" designs for a unique desktop look.
Learning Curve: New users may find window positioning and advanced customization (which sometimes requires editing XML files) to be unintuitive.
The core reason to upgrade is connectivity. The Pro license unlocks the ability to sync with the services you already use, ensuring you never have to enter the same event twice.