Yeah, just for looks mostly. I grew up in the 70's and 80's, and that was pretty much the flavor of the day. I watched movies on Saturday afternoons like The Green Beret's with John Wayne, and Missing in Action with Chuck Norris. I wanted one when I was a kid, and now that I can, I would like to indulge that want. Not sure when I will be able to do it. I just saw this nice looking FN-15 at a LGS and wondered if it could be done.
Also, they were usually the longer barrel back then too right? they look longer, I was just assuming the 20" barrel was the more common length, but I should know better than to assume, since I have been burned on that before.