A Gillet for every person travelling is a must have. Always, but always Stop at stop signs even if there is not a car in sight as Gendarmes have a habit of watching these stop places from hidden vantage points knowing drivers will think its pointless to stop when the road is clear - instant fine in cash and don't waste your time arguing. Also if you have radar detection and they spot it in your car then you'll be in serious doodoo. If its something they can't take out and stamp on, then it could be worse.
About the Mobsters car I've only just bought a Lexus and my W140 S320 Merc is probably more of a "Gangster car" but I've never been stopped on French roads. Only at the border control at Calais have I had an inspection. .When the rear window mechanism failed going over, and I couldnt repair it before getting back to the UK, so French Border Control at Calais were very interested as the window was nowhere to be seen, just cardboard and duct tape over the area. They asked me to open the boot and had a cursory glance. Usual tools and customary booze. Waved me to close it and I lightly pulled it down with the hand plate (no dirty hands on the actual boot) and of course it self-closed. The Customs Frenchman called me back to open it again as I think he must have thought there was some small person inside who had pulled it in, as it creaked shut. Laugh.
With regard to Deflectors I'm surprised that the Car Booklet doesn't give any diagram of the positioning of Deflectors? Merc book does. I always use Silver Duct tape and long ago stopped buying those things you get from the AA or on the ferry which are pricey and diffcult to remove the tackiness. Tape does the job just as well and is easily shaped by adhering a length to a piece of greaseproof paper first. Actually it can be cut more precisely to shape than those AA things.