Yesterday I designed, built, and installed a windscreen.
Last night I went for a drive, and found that while there is some improvement, it's not enough to get exited about.
Unless you desire the special effect ones with the etching and lighting, I would not pay full price for a windscreen, in my opinion.
Mine cost under $40, but 5 hours labour.
It removes or installs in 30 seconds.
I would like to see some wind tunnel results to support the claims being made.