I'm guessing regarding being able to use it outside of their apps, no? That's my main concern. I'm mainly a Mail.app user and having to run the bridge all the time does not seem ideal for me. I haven't tried it out so this is just me talking from the outside.
Search sucks: really. unable to find stuff unless you know the sender, their full text search seems to only work in a browser and only after indexing (which can take an hour) and it will go away with time as it's browser local storage.
Sending emails directly from share sheet in iOS failed twice.
Unable to add an invite to a calendar invite on iOS or in the Webapp (if invited by someone else).
Emails broken format when forwarding to someone else.
Long delay in delivering a simple email (to google and apple) at least three times.
The way that the emails are threaded. And that trash still shows as being in the same thread, instead of moving apart.
False sense of security as most emails are only encrypted on one side. And mine are visible on the other side.
Also just left Proton, there are so many small issues and annoyances in their iOS/iPadOS apps;
You can’t even search the content of e-mails. Can’t increase font size (pinch to zoom sort of works, but impossible to use on a small iPhone (Max) screen). Can’t set any custom notifications. Don’t see what folder an email is stored in. I can go on forever…
And of course it’s not a native app either.
It was a great relief going back to the stock Mail app.
I’ll happily return to Proton when they fix all the issues, and it doesn’t kill my productivity anymore.