Open whisper protocol works with a federated networks in fact its more anonymous cos if u have only one server u can collate senders and receiver’s to build a social graph. Their is quite a bit of sus shit related to signal they don’t like 3rd party clients, they have mandatory phone number requirements (despite that being their most significant cost), they received money from inqtel the CIA venture capital fund.

I don’t see what security advantage u get from a single vendor ecosystem. I see a lot a reasons it can be abused tho.