The overall rating reflects the current state of the app. It accounts for all app reviews but prioritizes the most recent ones.
The app works reasonably well for exporting some data that can't be exported any other way. However: really had a mess when I updated and re-imported. Sent a message to the support team ... haven't heard a peep from them since. So unless you want to scramble your data ... probably not a good product to do mass updates or any uploads.