The basic version of this app is free. It allows you to import your last 6 months of recently-created campaigns, up to 500 members per list, and up to 5 unsubscribers per campaign. To lift these limitations, you can subscribe for the Premium version here. The Premium subscription will allow you to import all historical data.
With both free and premium versions, the report layout can be edited, and the data can be imported or connected live via Excel and Power BI to build your own reporting tools from your Mailchimp data.