There are a lot of different systems, gravel guards, tow bar nets, vehicle bras, windshield covers, etc. There are pros and cons with each system . I have experienced a lot of gravel damage to my 2007 HHR toad requiring one repaint of the hood so far. I just recently started to use a Blue Ox gravel guard plus a windshield cover. I decided on a gravel guard instead of a bra for the following reasons: A bra is a hassle to put on so the tendency is to leave it on for long periods of time. This can result in your paint getting sanded from the grit and dirt that gets trapped in between the bra and paint. Also, the car should be clean before installing the bra. This is not always practical when travelling. Even if the car is wet and dirty, a gravel guard can be installed or removed without much effort. I then use a windshield cover, but only if I am able to clean and dry the windshield first. The cover is very easy to use.
I was told by a mechanic once that the easiest and cheapest system is to use nothing! Just repaint your hood and bumper after 5 years! Considering the costs of all the accessories, this might be good advise!