I am very impressed with their service, accessing it on their .onion site. I've been paying with Bitcoin, but it has been a manual process. Their support seems responsive. The UI is great.

I was going to use fastmail, but ProtonMail's inbox encryption seemed like a nice bonus. I know it is not really securing my email, but it is nice to know that if they get a subpoena or warrant they cannot just dump my inbox. At least not without compromising their product - an active step.

Setup of domains and accounts is slick. Changing payment plans all works online, pro-rating and all.