No, it's even less secure than expected. We expected that Sunbird would have access to your Apple ID and messages. Instead, everyone in the world has access to your Apple ID and messages.
Yeah, but I got absolutely roasted in YouTube comments for pointing out some potential shortcomings in the architecture. I’m not about to claim a high level of authority on the topic, though I’m an old man who has been in the game for a while, but the people that were totally confident really just seemed very eager to accept the passing of their credentials in a very sketchy way to get a slightly different messaging experience.
I don’t get the buzz around this. It’s a really ugly hack, it’s costing someone money to run those mac servers, and the longevity of the service is questionable.
Beeper is pretty good with it, as they make it clear that it's insecure and use an encrypted protocol to get the messages to the server. Still, it's better to host your own (which Beeper lets you do, as it's just Matrix) or not use it.
Due to complexity and limited auditing a number of vulnerabilites have slipped through again & again, like zero-click exploits for example. Take a look at the sear volume of CVEs and more importantly what they entail.
While they do eventually get found & patched, its not ideal compared to other messaging apps like signal that are very much security first, features 2nd.
A lot of people(normies), especially Apple users tend to think it's super secure virtually impenetrable technology.