Linux

Yeah, I do wish proton was more open about their tech. I do know that proton allows you to make free accounts without giving them identifiable info (which makes them a popular choice for scammers, which is annoying when services just block their email domain thinking it's always nefarious). I don't recall what the payment options are, but I'd be surprised if they didn't have any crypto/anonymous ways to pay.

I still haven't made use of the proton VPN, mostly because, yeah, I don't care for running a proprietary client for something like that, but also the last time I looked into it they did offer wireguard configs that would do the same thing. The client is just intended to be a familiar cross platform interface. No idea about this Stealth mode protocol, though. Seems like that would have to be run locally.

If you do pay for their email, I recommend bringing your own domain. 99% of the time the proton.me domain works fine, but for the 1% of the time when a system has a problem, it does make me wonder if there's somewhere in their system blacklisting their domain.

with the cooperation with law enforcement proton has stated to do

I'm curious what statements you're referring to. For a company to continue operating, they have to comply with local law enforcement to the extent the law requires. They don't have a choice. If you asked mullvad, they would say the same. But the point of all these services is that they (claim to) do their best to not keep any records by design, so that when law enforcement comes with a subpoena, they have as little as possible to hand over in cooperation. But yeah, as you said, at the end of the day we just have to trust that that's how they operate.