Composite balls with the NFHS mark are legal footballs. In many ways, they are superior to leather footballs, including grip, particularly in wet weather. In the future, it may be all you see.
In basketball, the only leather balls still used are in the NBA. Everyone else, from college on down, now uses a composite ball. Part of it is cost, part of it is performance. When I worked for Spalding, we created a composite ball for the NBA, and it was used for about 2 months. Players complained, but the biggest reason wasn't performance, it was image. As Paul Pierce (who was under endorsement contract to us) said, "Don't take away the leather ball. Playing with a leather ball tells us we made it. You only get to use a leather ball if you make it to the Show. Don't take that away."
The leather used in footballs is not as high quality of that used in basketballs, but eventually, the cost difference may drive leather footballs out of high school and NCAA play.