They are excactly what the name implies. Testing is generally pretty good, but it’s still testing. And unstable is also what the name implies. People, myself included back in the day, run both as daily drivers, but if you want rock stable distribution installing unstable revision might not be the best choise.
Not for everyone, but if you live in Finland you can (most likely) access National E-library. Unfortunately it’s only for IOS or Android, no e-readers are currently supported.