That was my thought when he suggested using Signal.

Sure it might be secure now but we have no clue if / when the app is infiltrated or even worse, could be spoofed and have a bad app pushed to our phones.

(Don't hang me. Just off the cuff idea, I have no clue if it is completely possible to do such a thing but it seems within the realm of possibilities)

EDIT: On second thought, don't you have to sign apps with a private key? I assume that raises the bar a bit, as long as the devs can keep those keys private which seems reasonable enough for such an app.