I have Performance's house-brand bike bra and it has been fine. I've used it on long trips and at 70+ mph highway speed and it has held up with no problems. Be sure to pull the attachment points tight and tuck in or tie off every loose end to avoid flapping and noise as well as possible damage to the paint (bike or car).
However, these things make an already poorly aerodynamic item (a bike on a roof rack) even less aerodynamic so expect some additional drop in gas mileage.