Might be a strange question for the Bicycle Mechanics forum, but my first stab in Road Cycling disclosed that nobody with a road bike uses one of these things. I have a tandem and I'm not buying a new car just to fit my tandem inside the vehicle so a bicycle bra looks reasonable if they are durable enough.
I'd be interested in user experience with bicycle bras similar to Sci-Con. They certainly look like they will protect a roof-mounted bike, but do they hold up at highway speeds (75 mph in California)? I wouldn't use one for a short transport, but for anything over an hour our anything through the bug-riddled Central Valley these things look like good ideas. I assume they are washable 'cause they are going to get very, very messy.