Would be great to have some options for duplicating view of a monitor. E.g. duplicate view of main monitor to TV. Unify screens is not an option if there are more than 2 monitors and you only whish to duplicate one.
You can just move the screens you want to duplicate on top of each other. I can't think of a better way to do it in the current UI.
Well, that sounds like a good way to do it. However, I did not find out by myself, so there is clearly a lack of documentation. If you're interested I may find some time to help you with that.
Yeah, this was the original way of cloning screens and people complained that it's really really hard to discover, that's why we added the "Unify outputs" button. We used to have a tooltip IIRC, but I guess it got lost during Plasma 5 transition.
This is something better suited for the full KCM. The little applet is really only able to do fairly simple things, and I think we can't overload it too much.