FWIW, many of my friends actually could say this, for I am a programmer who's not on Facebook/WhatsApp and recommends Signal.
It definitely needs to be more reliable, though. The last time I tried to call someone with Signal instead of just using it for messaging, I got a ringing indication but they heard nothing and then after a few seconds the call showed up as missed, and the same happened the other way around with them calling me. There seem to have been about 500 updates to the iOS app in the past 5 minutes via the app store, though, so many whatever caused that was a short-lived glitch.