The overall rating reflects the current state of the app. It accounts for all app reviews but prioritizes the most recent ones.
We wanted to test it but decided it was not for us, once we uninstalled the app, but it screwed up our theme.
We had to call Shopify to fix it. At the time there was no intention that you had to do more than just uninstall the app. The developer continuously emailed us asking us to change the rating but our review is not with the app but the uninstall process. I want to make it clear, we did not use the app!
Our issue, it removed the standard drop-down for customers to select a color after uninstalling the app. Luckily Shopify was able to fix it for us.
However, we can say this, the developer responses fairly quickly so if you should have a problem he will be available to help.