We are a Pro customer and recently set up an s2 member site where we offer a free level and 3 paid levels. We need to integrate s2 with Mailchimp so that each member level gets synched with a Mailchimp Group. This doesnt work now with the current s2 settings. subscribers dont get automatically added to groups.
I recently tried Zapier with another cloud based app to link it to Mailchimp and it works great. Zapier has a very user friendly dashboard and all the settings you can control to make sure the databases synch and your users dont get unwanted confirmation messages and optin requests that are built in to Mailchimp. Can S2 please consider becoming an app on Zapier so we can build a S2>Mailchimp zap. Thousands of other connected apps are already on Zapier and this would make life so much easier for s2 users. There is a Developer platform for you to do this here: https://zapier.com/developer/
I am including a screenshot here http://bit.ly/2q8eRuZ so you can see how user friendly the settings are in Zapier once an app is connected.