Flume Pro is an upgrade for Flume that includes additional features, as well as helps sustain future development, bug-fixes, and customer support. The features unlocked with Flume Pro (at time of writing) include:
You can purchase a Flume Pro licence from flume.app. You will receive a Flume Pro licence code after checkout, which can be used to unlock Flume Pro's features - no separate download of Flume is necessary.
Note: Flume Pro licences are one-time payments and not a subscription.