It won the Levchin Prize at Real World Crypto, and is essentially the gold standard for messaging cryptography. People on HN hate its ergonomics. You could reasonably prefer something else, but you can't reasonably call it untrustworthy.
I don’t really know why, even. I get the account vs phone number argument (though I prefer phone number as it is familiar to regular people in a way that usernames are not) but aside from that it has every feature I could want, and I feel like I am a fairly demanding user. It is is my primary messaging app and I send hundreds of messages a day to my friends, both individually and in group, on my phone and on my desktop.
Transacting in phone numbers doesn't feel right to people who have been soaking in message board and IRC culture for (in some cases) decades, even though it's absolutely natural to ordinary people (remember, WhatsApp was for a very long time the most popular messaging service in the world).
And those same people have very strong feelings about services where you can't build your own client from scratch, and a viscerally negative reaction to Signal's principle that open clients create a lowest-common-denominator anchor for security. I get that too, even though the point is kind of indisputable (see: what happened with Matrix E2E crypto).
Signal has a clear vision for how security and privacy work in messaging, and they're uncompromising about it. I deeply respect that, since there are a lot of things they could do to pick up Internet points that they don't do because they haven't worked out the privacy details yet. But opinions differ.
I get that (I grew up on IRC and with an ICQ# too) but it does massively simplify the onboarding process - both because it’s familiar to WhatsApp users (of which 99%+ of people who get signal would have previously had WhatsApp) and because you immediately know which of your contacts already have signal.
