I just tried the app via the US App Store and it requires you to verify through SMS before use. This means that it’s neither anonymous nor fit for use in a disaster zone. Good example of software that would be better if open source.
Combining mesh over some/several form(s) of 802.11, Signal protocol public key distribution "locally" via QR code, and Delay-Tolerant Networking (Cerf et al. 2007) would be the holy grail (and would have no reliance on SMS or phone number) and also could not be monetized. Which is a damn shame, because it's eminently technically feasible, but complicated enough that I'd probably need a professional team to implement.