The overall rating reflects the current state of the app. It accounts for all app reviews but prioritizes the most recent ones.
I really wanted to offer extended warranty for my products. Unfortunately, it was not a match made in heaven. Given my lower price point for the niche and focusing only on mobile audience market, as soon as I launched, my conversion dropped completely and upon deleting the product, the sales picked up again. YMMV. Personally, I always purchase these warranties and benefited from it. But my target audience see otherwise.