So there are two big issues with #Signal that make it unsuitable. The first one is that they don't federate, so users are perpetually bound to their servers. Users may use it and enjoy it and recommend it, but if OpenWhisper Systems (or whatever their current name is) decides to close down their servers, users are screwed. Second, is that they require users' telephone numbers. Now, I suppose this is because they act as a text message delivery system (only using the data plan instead of the carrier's SMS plan), but it does mean that as soon as someone figures out how to pierce the encryption, all those "secret" messages are now directly attributable to the person to whom the corresponding telephone number was issued.

On the other hand, I do see @rysiek posting about using and recommending Signal when communicating with whistleblowers and other news sources whose lives and freedom are at risk if $GOVERNMENT or $EMPLOYER were to ever discover them. He's convinced that when lives are in danger, Signal is the only messenger he trusts.