Proton is great but lacks integration with Android (and others)
Proton is intended for (extreme) privacy and I get it. This is very good and terrible at the same time : the vast majority of your apps provide no possibility to have a smooth integration with the ecosystem they live in :
- Calendar : impossible to have my events in the Android calendar with my other accounts. Calendars can't be shared so that people use a common calendar for common activities.
- Contacts : impossible to have my contacts in Android so I could use them with the dialer
- Drive : no sync client for Linux, Windows, MacOS
Why aren't you providing an option to opt-out from some privacy ? Not everybody needs extreme privacy.
Because of that, normal people (and me) aren't going to use your awesome services : there is a too big usability gap comparing to Google and the others.

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Draven “Xarcell” Vestatt commented
To ask for privacy is not extreme. Either a product offers privacy or it don't. If you don't want privacy, use something else.