I am going to install a new head unit when i get a Blazer, and i was wondering if these Antenna boosters are any good. go to http://www.crutchfield.com/cgi-bin/S-1jheZXC3P0V/ProdGroup.asp?c=2&g=732&s=0 to see two. Has anyone installed these? How do they work? Do they just make it louder, or actually improve reception? Thanks!