The overall rating reflects the current state of the app. It accounts for all app reviews but prioritizes the most recent ones.
Don't pay for this app! The description states that the Sale Price and Additional Image Link would be included, but it wasn't. In addition to this, the description field ended up showing the Shopify product tags instead of the actual product descriptions and there aren't any mapping options to fix this. There are better apps out there for this purpose at a similar pricing...