I have to use a computer and my cell every day for work. Truth is all those terms, conditions, privacy policies and app permissions are just CYA for the NSA. If you use your phone or PC they are watching. If you have agreed to those vague terms of “we” have permission to access/ monitor yada yada yada they are covered. If they want my info they are going to collect it. Nothing I can do to stop it. That is why I prefer physical assets. I have control and possession of them. It’s the best I can do. As far as being hacked, not much I can do about that either. They hack my bank, the bank covers my losses. That is also why I don’t keep all my money in the bank.
As far as the app goes I have found a little more info.
Looks like there was a little misinformation about zello. It has to have cell service or Wi-Fi, so it will work if cell service is out but only if you still have WiFi.