On its 10th anniversary, Signal’s president wants to remind you that the world’s most secure communications platform is a nonprofit. It’s free. It doesn’t track you or serve you ads. It pays its engineers very well. And it’s a go-to app for hundreds of millions of people.
You don't have to take Signal's word for it, because it's been audited. The EFF, who are VERY privacy minded, and do extensive research into this type of thing, recommends Signal because it's known to be secure.
No support for Monero despite it being requested on uservoice 6 years ago. A Bitcoin wallet (seriously?) which is easily traceable. Important email metadata is also not zero access encrypted (i.e., subject headers, from/to headers) which leaks a substantial amount of information even if the body is encrypted. Not to mention they had clearnet redirects from their onion service a while back, something a lot of honeypots usually do.
Even if it's not a honeypot, you're sure as hell not getting any privacy with Proton. That's for sure.
You can't e2e the to and from headers in an email. that's a problem with the protocol, not with proton. I'd assume the subject line falls into a similar bucket, because mailservers probably want to use it to filter spam