I can attest that all of the Kodiak-based platforms are solid. They meet Mission Critical standard, and are about as reliable as you can get for PoC comms. These options include Motorola WAVE OnCloud (the most flexible), Sprint Direct Connect Plus, Verizon Push To Talk Plus, and AT&T Enhanced PTT. With the exception of the Motorola product, all of them are locked to carrier dependency, so you can only talk to other users who have both the service, as well as the same carrier, as you. The only way around that with Kodiak is to use Motorola WAVE. It should be noted that Sprint, Verizon, and AT&T all claim that there is carrier interoperability, and that non-carrier members may use the service, by adding a "cross-carrier account". To date, in extensive talks with all 3 carriers, none seem to have any idea how to do such a thing, and all are surprised to hear that their company states that it's possible in advertising materials.
Also, all of the Kodiak options operate as a dedicated corporate account would operate. You can manually input contacts you wish to communicate with, no problem, but it's all based on a corporate web portal, where you can add and change designators and accounts, much like if you operated, say, an ambulance service, or a delivery company, or something along those lines.
Zello for Work and ESChat also operate along these same lines, although IMHO are less stable and less effective than Kodiak. It appears that T-Mobile, being the outlier among major carriers, has a tie-in with ESChat.
Standard Zello can definitely be confusing when you have a lot of contacts, and if you're trying to get multiple people onto one talkgroup, it can also be a hassle. Ideally, you'd want a talkgroup to have password protections, and Zello loves doing that thing where you set a password, then go to put that password in, and it doesn't work. This wouldn't be required, if Zello weren't also overrun with a bunch of kids that use it for gaming, so no password = eventually some teenager will get into your talkgroup and just start shouting nonsense.
Still, the free Zello is likely still the best option for PoC communications, if you really don't want to pay for anything. Quality costs money in nearly all cases, and this is no exception.
