I’m not talking about the premium key sharing feature, that works as it should.
But in the free version you under File -> Key Management you can export your own and import another persons Public Sharing Key. The tooltip there says ‘Ask your contact to export and send his/her Public Sharing Key to you and import it here. Then you can share encrypted files.’
Because this is available in the free version, to me it seems as though you should be able to use this to share encrypted files with others without using the premium key sharing feature, albeit in a more roundabout and difficult way.
Otherwise, what is the use of this function if you can just share a file by typing in someone’s email??