This plugin does tracking/grabbing properly by tracking the data by localstorage only, rather than cookies or session variables. This is a superior way of tracking this data as it does not impact your server or break caching in any way.
It does so by including the Bill Franklins fantastic lightweight JavaScript library for this. I will be including thiis data automatically in my own plugins. But you can access intrsuctions and examples on how access this data in your own opt in forms here:
https://github.com/bilbof/purser