Got my invite and downloaded the app. It's really cool. I felt a bit uncomfortable with the account access needed, but its required for what they need to do. Essentially they need Gmail read access to scan your e-mails for receipts, and your Amazon login for order info. You don't have to log into your credit cards, you just select which credit cards you have and then select which card was used for which purchase.
Basically checks if you can get price protection if the price drops (they've automated it for Citi and Chase cards), and tells you how many days left you have to return items you've bought, and what your warranty status is on anything you've bought (included extended warranty from credit cards).
Not surprising that Google doesn't have a single user review, they just got funded and just released the app.
I e-mailed the team because they don't currently support 2FA (two-factor authentication) on Amazon, but they are planning to in the next build. I told them I am an iOS developer, so they are going to send me the Beta build to test.