This not being an official release from Google, using this is potentially worse than giving someone your Google password without fully vetting it. There are some existing safeguards in place to make a password alone difficult to use, but the app itself would have signed in access to your account and the contents of files. You may think it's simple to watch the app for bad behavior and decide it's safe, but you wouldn't be thinking deviously enough.

Nothing against the developer as they may be trustworthy and honest, but don't make the mistake of assuming that someone bold enough to put out something that requires that much trust must by extension be worth trusting. People too often do.