Rethink isn't quite ready yet. Depending on your use case you can go without getting thrown off by a bug for weeks, but when it fails it can be quite annoying. And don't use the GPlay version, but the FDroid or GitHub one.

On the other hand, the functionality is top notch. Easily the best integration of consumer level DNS + firewall blocking in any application on any platform. Just block everything of an application by default and then watch the connection logs for the app and start unblocking stuff via ips, domains or wildcards until the app starts working again.