I’m sticking with Signal… it’s very popular! They are a registered US non-profit so if you itemize deductions, you can include your Signal donations. Fun fact… early Signal development received $3 million from the US government–sponsored Open Technology Fund.
Despite what you hear in the news, Signal is not pre-installed on any old device left laying around and available for anyone to use ad hoc. A master Signal instance is installed on your mobile phone and your Signal account is created/registered/personalized to your phone number at the time of installation by way of SMS text verification code handshake (the rational for using your phone number for your Signal account ID). You can then set Signal to not reveal your phone number to anyone Period (the two settings are Nobody and Nobody). Instead, you can create and use disposable username(s) by which to establish your Signal contacts. I suggest not granting the Signal app permission to access your Android Contacts to prevent it from elevating those it identifies by their Signal account phone number to become Signal Contacts… you most likely do not want your many Android Contacts to automatically become your Signal Contacts especially if one of them happens to be Jeffrey Goldberg and you are Michael Waltz. You can always give Signal permission later to access your Android Contacts to find those contacts using Signal with their phone number NOT hidden (not recommended).
You can not use Signal to communicate with a Signal Contact/anyone until that contact accepts your invitation or vice-versa, one-time. You can subsequently revoke/block any contact. You can also use a Signal tool to verify that a connection with a contact is fully secure. The primary insecurity of Signal, like everything else, is the security of the endpoints… someone using your phone as you. The actual Signal data store on each endpoint is encrypted.
No ads on Signal. Ad networks are being used to deliver phishing malware… malvertising. Block ads… don’t install them. It’s unfortunate(?) that website owners have every incentive to allow the ridiculous and malicious proliferation of any and all ads… they get ad revenue if you don’t subscribe and they get subscription revenue if you do… and some will try for both, if they can get away with it.
Given Signal in the news, I would not be surprised to hear that it crashes soon due to everyone rushing to use it. If so, give them a little time to scale up and recover.
OE