I am very happy with the panels I bought from GIK a few years back. I bought four more to treat the ceiling and after trying every configuration I could come up with ended up with just one. It's centered halfway between the speakers and the listening position. The other four were added to the front wall.
I hauled a few over to my brother's place to experiment with. He has Cornwalls.In his room there is obviously bass build up in one back corner which was smoothed out when we propped up the panels there.He didn't like how they looked though. I'm going back one of these days and show him some nicely treated rooms that I'll download. He (gasp!) has no wifi:-)