My preference is to double one earthwire then park it under the box earth terminal before it continues to the socket earth terminal rather than create a separate earth tail.
I do not like reliance on the fixed lug - folk often slacken off the faceplate screws and don`t quite tighten them back fully, or they become a bit loose overtime, can create a poorer connection.
So, although it`s often not needed I do connect the back box earth terminal usually by doubling but sometimes by fly lead instead.
I have seen, for some reason, the fixing screws replaced with nylon screws. The mind boggles - I don`t just mean on plastic lightswitches and unearthed lighting circuits but on socket circuits too
