I agree that Tox is better but at the same time I know people who truly need to stay hidden and they use Signal on a burner phone with a cash sim-card. That way it doesn't matter which medium the messages are transmitted over because it still can't be traced back to them.
And as far as I know the encryption is solid.
Unlike some other alternatives like Wickr Signal actually open sources their app and their communication protocol.
Until Tox defaults it's communication through Tor, it doesn't offer any notable differences. Sure, there is no central server, but intelligence agencies can see who you talk to without compromising server just by looking at the destination IP address of packets. Tox suffers from same MITM problems if the ToxID is changed e.g. on Twitter page of your contact, the same way the author of the article claims the "checksum" of Signal's APK can be changed by NSA, your employer or angry spouse.
And as far as I know the encryption is solid.
Unlike some other alternatives like Wickr Signal actually open sources their app and their communication protocol.