Those who know the "developer" behind it won't touch it with a six-foot pole.
I wouldn't normally criticise people anonymously, but the guy is full of hot air, his only real skill being knowing how to play the media for hype. On the other hand his technical incompetence is legendary, as when an early version of this signal application was just leaking all the stuff in plain text through the system logs or when he set up his "Google anonymiser" that he controlled, with no proof whatsoever that he wasn't himself doing the sort of snooping he accused Google of, and got cut off by his ISP for providing fake WHOIS details. And as has been pointed out above repeatedly, this supposed "privacy" application requires Google services so that it can collect usage stats, as mentioned by the "developer" in one of the discussions as to why he won't allow it to be distributed on F-Droid.
They conclude that it is impossible to say if Signal meets its goals, as there are none stated
Truly professional engineering, eh? Good thing the guy did not decide to take up aeronautics for a career.
Really, he should just go and become a PR consultant which is what he's indisputably good at.