This add-on will add an option to the checkout page that allows users to signup for your Mad Mimi newsletter at the same time as purchasing. As just a simple checkbox, this is guaranteed to create more newsletter sign ups than a regular subscribe form placed elsewhere on your site.
In the Misc section of the Easy Digital Downloads Settings, you will have options to enter your Mad Mimi email addres, Mad Mimi API key, choose the email list to subscribe users to, and an option to define the checkout field label.