I haven't looking into the Primacoustic panels, but I've been following (or trying to follow) the acoustical treatment at AVS for a while now. Some products look great, and work well... Some work well, but look "ghetto", and some look great, but don't help much.
The material used is the biggest factor. Well, that and size and placement. A single 12"x48" panel might be too narrow (only 12") to "catch" enough sound from reflecting. It might take 2 or more panels side by side (24" x 48") to make something that absorbs sound before it bounces back into the room.
2" panels seem to be the best compromise of thickness and aesthetics. Some people go 4", but those get to look pretty big some times. Also, the general consensus is to leave a small air gap behind the panels if possible to boost some performance, but I don't know how many people actually do that.
I am going to try going panel free in my room to see what happens. Bass traps in the front corners and the whole front wall behind my speakers and screen will be treated. I will see if it sounds the way I like, and if not, start looking at those first reflection points. I don't want to make the room too dead.