Considering that the entire selling point behind Signal is that it's supposed to be resistant to "an adversary like the NSA," I would think their ability to trivially associate a key with a real person would kind of turn that on its head.
Any global passive adversary can do traffic analysis on any communication network. Signal's message encryption should stand up against the NSA unless there are any vulnerabilities in the implementation that the NSA has found and not told anyone about or unless they have some magical decryption power that we don't know about (unlikely). Protection of metadata is much harder. If you connect to the Signal server and they can watch your network traffic and that of other Signal users, then they can infer who you are talking to. If they can send men with lawyers, guns, or money around to OWS then they can coerce them into recording when your client connects and from what IP, even without this.
In contrast, Tox uses a DHT, which makes some kinds of interception easier and others harder. There's no central repository mapping between Tox IDs and other identifiable information, but when you push anything to the DHT that's signed with your public key then it identifies your endpoint so a global passive adversary can use this to track you (Tox over Tor, in theory, protects you against this, but in practice there are so few people doing this that it's probably trivial to track).
No system is completely secure, but my personal thread model doesn't include the NSA taking an active interest in me - if they did that then there are probably a few hundred bugs in the operating systems and other programs that I use that they could exploit to compromise the endpoint, without bothering to attack the protocol. I'd like to be relatively secure against bulk data collection though - I don't want any intelligence or law enforcement agency to be able intercept communications unless at least one participant is actively under suspicion, because if you allow that you end up with something like Hoover's FBI or the Stazi..