Instead of making Cloning for everyone, maybe an avatar creator or someone using an avatar can set the avatar for friend cloning only
I agree with BadWolf, it should have similar functions to the instance types. though having it friends+ would be pretty much the same as having it public. you just have to be friends with one person who has the avatar to gain access to it.
It would be nice to have more options, I currently make avatars for friends and the cloning feature is way more conenient for sharing it with them, rather than needlessly making a private avatar world.
Or maybe alternatively, have a selection of choices for cloning like "Off, Friends, Friends+, Everyone" in the form of a dropdown or "next" type choice box.