Inside Blender go to the "Edit" section, and inside go to "Preferences", in the Add-ons sub-menu, go to "Install" (Upper right part) and there search the compressed folder called : Scatter-BETA-Assets-Tool.zip

You have two channels:

1. Inbox Blender marketplace (Email)
2. GitHub issues: https://github.com/BETAPANDERETA/Scatter-BETA-Assets-Tool/issues

There is no difference, just in free version the grass Scatter don't count inside the tool, just the Pay version had the Grass Scatter tool, however in blender marketplace I decided to put a price on my work if you want to value it, this would motivate me to make updates and other add-on's, of course paying for the add-on is optional, you can download it for free and enjoy it. In addition, 10% of each sale will be donated to the blender foundation.