Today every users can register any devices without any restriction by default, if you restrict user's devices he can't register any new device, this is very complicated to manage if you wants restrictions.
Without restrictions, a user can push averything he wants to any other user's devices via the DOWNLOAD TO button. see https://emby.media/c...-every-devices/
my suggestion is :
- only admins can push everything to any devices (I transcode and push kids movies to my ipad from my laptop or iphone for children offline watch)
- restrict DOWNLOAD TO fonly for current user's devices