I would never rely on a closed system for secure messaging to many unknowns.

Agree. Peoples are trusting App with unknown source code & delivery path, infrastructure controlled by 3rd party. Application cannot protect against OS and OS cannot protect against HW. Too many known unknowns. Seek the arguments how and why OTF got re-funded last time.

And yet iOS is probably the most secure mobile platform for secure messaging. Especially in lock down mode.

Except, you cant really verify all of that. so IMHO that's just speculation based on the surfacing of news which can easily be distorted. Or maybe you can. Is there any sources on people that have evaluated the security of these features.

You can’t verify that even on an open OS as there will still be closed hardware blobs. At least with popular systems there’s a lot of state level hacking activity so zero days get patched routinely. Also Apple has a program for researchers where they get more access to the system (That program was criticized heavily though for the way it was implemented).

It’s not a perfect system so right now you still have to trust someone at some point in the chain.

> At least with popular systems there’s a lot of state level hacking activity so zero days get patched routinely

Not sure how you're implying one leads to the other.