Any idea how it compares to Signal? They should be essentially using the same protocol. I also used it with good results with slow connectivity, but never tried on bad 2G...
The encryption protocol is fairly unrelated to how an app handles poor connectivity. It’s a bit like comparing different websites handling poor connectivity differently even though they are all served over HTTP.
I have tried to use signal in a location that had voice, but no data (a very old, very rural tower in the middle of nowhere) a few years ago, and signal was completely worthless. Even though it can read and receive SMS, it seems to require a data connection to send..
I believe their communication layers are fairly different – WhatsApp used to use something based on XMPP at least until a while ago; I'm not sure what Signal uses, but I vaguely remember it being based on HTTP?
Can definitely be, I never investigated in detail, although I used alternative open source clients for both (signal-cli and a long time ago yowsup), so the information should be in there...
I hoped that Signal's use of HTTP was as a fallback in case a direct connection could not be established to use a more "compact" protocol, but I possibly don't remember correctly what I've read...