Xabber VS Lora-Chat-Device

Depending on when you last tried xmpp you might have experienced the OTR hell, which was never really codified 100% and spawned subtle incompatibilities between clients leading to weird and nondescript errors that never got addressed. Nowadays the popular clients support omemo (https://conversations.im/omemo/), which makes encryption just work™ out of the box and without hassle. The only exception to this is xabber, who are apparently afraid of law enforcement destroying their lifes should they implement proper encryption and also feel no need to support it anyways: https://github.com/redsolution/xabber-android/issues/540

> then try to find your contacts again (which may be cached by your client or not)

You can save XMPP account IDs in any mobile address book.

> Finally, you have to convince "someone" that this is just you with another account on another server. There is also no verified E2EE anymore.

I'd pretty much just do a video call at that point.

> How is this different from "when Signal goes down one uses a completely different instant messaging system", apart from using another client?

You don't have to use another client software.

> Which means: If one of these hosting companies blocks XMPP traffic (e.g., if a rogue state starts censoring) or one of these XMPP servers goes down, a huge part of XMPP users is affected.

Equally applies to most messaging apps out there. Some XMPP apps have the benefit of also supporting using Tor and hidden services - Signal/WhatsApp/etc, don't.

Don't want to use the Internet at all? You can even go wild and do something like: https://github.com/ddamianus/Lora-Chat-Device - I realize this is something most people would not do, but XMPP's _flexibility_ allows this to be an option if it was something people wanted. Can't do Signal over LoRa.