I can certainly see how it would be very useful, like you said, in coordinating over long distances BEFORE you go off grid so to speak or hit areas where LTE coverage is spotty (wich is A LOT of places in the NW, even along main roads). As for the other comments, I think your first sentence is a bit confusing and seems to imply that Zello can be used in an off grid situation.
That said, my father in law tried to get me to use it. It worked well but kinda felt like a solution looking for a problem. And where you mention that critical services and such are moving to using Zello for communication, I'm not sure that is accurate (could be wrong though). Most business and government services in Europe and here in the US use DMR, which is an internet based digital radio protocol. Its similar but does not rely on civilian LTE coverage and therefore will be more reliable in a disaster (read the LTE network will be flooded and unreliable with customers trying to contact loved ones, where as the DMR stations because they use thier own equipment to get into the internet will continue to function like any other day). Government was what DMR was originally developed for, us Hams just stole it, lol.
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Well, I just retired after a thirty year career in law enforcement and I can assure you that it is being used. ESChat is used by many departments including AMR Ambulance all across the United States. My unit used Zello to coordinate detectives all over Southern California. LTE services can have tiered priority for public safety and even when they don't the reliability is so good it nearly always beats LMR systems. During the pandemic I set up a communications system at a vaccine site that had thousands of users in an area the size of a high school and there was no network slow down at all. Voice data takes almost no spectrum at all.
My collateral duty at my department was communications and I worked with public safety agencies all over the state. There is technically no "standard" for public safety radio systems in the United States. P25 became an APCO standard and at one point the Federal Government would issue grant money to agencies deploying P25. That money is long gone and now agencies are doing all kinda of things. Inyo County is in the process of going to an LTR trunked system on a private network. Mono County uses ESChat for their Fire and Sheriff's Department. In Europe the primary radio system type is TETRA not DMR. TETRA is being phased out and is being replaced by ESN which is a form of Mission Critical PTT over LTE. I never said Zello could be used off grid and never implied it in any way shape or form.
Look, I don't get what the argument is here. I suggested people look at Zello because over long distances its free, its easy and it works. It works so well that many trucking companies no longer even allow CB radios in their trucks, but they allow Zello. If you don't like it, don't use it, I don't really care either way. I was just trying to help some people because I have a lot of experience in communicaitons, both from the military and then later in public safety. After this, chances are I will never try and assist anyone again.