I gave it a 4/5 only because some critical updates are late in arriving or becoming available for the free version. Captcha was a pay only feature for a while. Also, I know the 2.5 version is coming later this month, but ...
Having said that, the 1.7 version does appear to be stable on 2.5, so I'm moving forward with that in my development/test environment until the official 2.5 stable version of CB is released.
Overall, CB is great extension and highly recommended. If I was doing more professional projects that create revenue streams, I would probably do one of the pay subscriptions.
The extension also integrates seamlessly with CB. Upgrading has also been a breeze. Thanks!