The overall rating reflects the current state of the app. It accounts for all app reviews but prioritizes the most recent ones.
This system is retarded, you have to manually go and refresh "update all stores" when orders come in to make sure the orders get pulled from Shopify and then pushed to FBA. The goal of having such is a system is to automate a process and not use manpower, but you still need manpower to update orders.
I've had less than satisfactory results with Shipstation. It takes a long time for the program to enter and have high-speed Internet. The user interface is less than intuitive. Overall I think there has to be a better way, I just haven't found it yet.