bra= Yes 
Hate the damage stone chips do... Just remember to keep it clean underneath and don't leave it on. 
For motorway trips for me I use it, another then that, it's off the car.
Problem is it realistically only protects a small area, not your windscreen (obviously) roof, wings, bumper (that's a big one) or the top of your bonnet. Sods law says that if a stone's going to hit your car, it will be somewhere that the bra isn't protecting.

In addition to this, on my previous 2 cars (not incl the GTI) there have been four really bad "stone" chips on the paint. One was at the top of the bonnet (by the windscreen), one was on the A pillar, one was on the lip of the roof just above the windscreen and one was on the door, which was so bad I had to have it resprayed. In addition to this, I had a large stone hit my windscreen which resulted in several cracks. I haven't (touch wood) had a significant chip anywhere near where a bra would be.