This subject has been discussed on just about every RV forum on the web, and there are over a dozen RV forums at my last count..
Some folks like them and some don't.
But unless you understand how they are "Supposed" to work, you are wasting your money installing one on your tow vehicle..
Here are a couple of links to other discussions on the subject of wind deflectors..
Maybe reading what others have to say about their experience with wind deflectors will help you in your decision..