If you are using clone (not duplicate), you don't have to keep cloning and flipping; the changes are live - try to modify left object in attached file. You can also use rotation, to achieve rotation of imaginary mirror-line.
The line tool you suggested, would bring only one thing new - the automatic clip on the line (but you can still do it through clip tool in limited way). Maybe it would be better to improve functionality of clip tool.
If you are using clone (not duplicate), you don't have to keep cloning and flipping; the changes are live - try to modify left object in attached file. You can also use rotation, to achieve rotation of imaginary mirror-line.
The line tool you suggested, would bring only one thing new - the automatic clip on the line (but you can still do it through clip tool in limited way). Maybe it would be better to improve functionality of clip tool.