What is the difference between Mermaid & Siren?

The mermaid and siren level subscriptions have exactly the same access to exactly the same content. Both levels have access to absolutely everything and all of the exclusive features across the network. The mermaid level membership is a monthly subscription and the member is charged each month until they choose to cancel. The Siren level membership is a reoccurring annual charge, and this member is charged once per year until they choose to cancel.