Seriously, what are you talking about? The vast majority of people don't want anonymity. Obviously Signal isn't cut out for that! The fact is, most people don't care about anonymity.
And what metadata can you harvest exactly from a UNIX timestamp and phone number? Signal can tell who is communicating to who, but they cannot read your messages.
When you use a client, you are relying on the client's crypto implementation to be correct. This is only one part of it and there's a lot more to it when it comes to hardening the program. Signal focuses on their desktop and mobile clients and they hire actual security professionals and cryptographers (unlike the charlatans in this thread) to implement it correctly.
Having third party clients would not definitively mean the client is bad, but it most likely would break the security model. Just take a look at Matrix's clients.