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.
+1
I've never really understood the concept? My way of preventing stone chips has always been not to drive up the arse of everyone and works for me?
I wish I could say the same. I never, ever drive up anyones arse.. for several reasons, but stone chips are a big one.... and I think I've been really unlucky with them in the past. I see someone driving a nice car and more often than not, driving really close and I wonder, "do they not care about chips? or crashing?" but I take comfort in the fact that when someone drives up my arse, hopefully I will flick some stones up and that will teach em. Oh and a little blast of the washers works wonders too
