The overall rating reflects the current state of the app. It accounts for all app reviews but prioritizes the most recent ones.
I used the app to copy one store and keep it updated on 2 destination stores and it works great. Even the themes were copied perfectly. The only reason I don't give 5 stars it's because you have to subscribe in the source store making it a very expensive App to keep.
Replay has made the seemingly impossible task of maintaining and syncing multiple e-commerce stores (product info, inventory etc) possible.