L/C 100 Series "dust deflector" Does it work?

Evening all; We have a 600 metre dusty gravel driveway to the main bitumen road and the dust always settles on the rear window and back of our vehicle. Its the only place (in the summer) where our vehicle gets dirty. Can anyone tell me if the dust deflector that sits on the roof over the rear door works. The Toyota salesman said they don't.

Thanks, Philip.