I looked at Dino and another one mentioned here and they look dated. Windows 95 feel with better anti-aliasing, rounder corners, but same colors? Gtk 2 or something?
Looks like a standard GTK4 app to me. Whether or not that is to someone’s tastes is obviously subjective, but it uses the same design language as every other GTK app under the sun.
GTK apps always look out of place on Windows though. Looks far more sensible in its native environment (i.e. *nix running GNOME).
The UK isn’t quite that far, but it’s absolutely the dominant text messaging and calling app in the UK. Nobody uses the built in Android or Apple tools anymore, and I’m as likely to receive a WhatsApp voice call as an actual phone call these days.
I have Signal on my phone, but I’ve literally never had a cause to use it; I’ve simply got no contacts on there.