Integrating iPad with non-Apple world

all apps downloaded from app store should work fine

if you somehow use an unofficial way to get apps not from the app store on to your ipad then it's everyones best guess which ones works well

Proton is not an Apple application.

Any issues with Proton or how to use Proton, you will need to contact the developer of the application.

There's no problem setting up several e-mail accounts on an iPad – pulling in e-mail and calendars from multiple sources such as iCloud and Gmail. You can have iCloud Drive, Google Drive, and Microsoft OneDrive. There is a fairly large amount of stuff where, if you want to pile on stuff from multiple vendors, you can.

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The one that you need to watch out for is mixing anything else with iCloud Photos. When you use it, a request to delete a photo from any connected device (iPhone, Mac, etc.) is taken as a request to delete that photo on all of your synchronized devices, and in iCloud.

So what happens if you synchronize your iPhone's Photos library both against iCloud, and against Google Photos? Then run low on free space in the Google cloud, and start deleting photos from your iPhone, thinking that you are "only" deleting them from Google Photos or from that iPhone, and that they are safe in iCloud?

That's right, you'd be deleting your photos from iCloud Photos and every device that synchronizes with it …