Like sharing your WLAN. It works great between iPhones,
if you know how it works and the preconditions are fulfilled (it's undiscoverable). You can't share with Android devices by showing them a QR code – which I would consider the "usual" way and which is easy to do on Android devices.
Edit:
Here is the procedure I was talking about and all prerequisites for it to work:
https://support.apple.com/en-us/102635