Forward cabs - Do they work?

[Tomk26B4]

Everyone seems to using forward cab shells now, considering the shape of them they should give more front end.
I was wondering how fast does the car have to be going to feel a difference, does just works in sweepers?
Also is it just that it only really can benefit the top drivers and everyone is copying thinking it will make them drive like Lee Martin ect, or is there a clear advantage even for club drivers?