My experience as a long time apartment dweller, and now home owner, was that the GIK products I have travelled very well from place to place. The broad band soffit traps have been especially effective and beneficial.
I do think the pro calculators ask for excess treatment, but each room and space is different. In my case with modest sized rooms they have worked really well and in fact have outlived every other piece of stereo gear.
I have six more units coming in march. A pair of corner traps and four 4" thick bass traps to cover the bay window which is where the TV lives. The view is to my neighbor's window so covering this up is fine.
I'll post when they are in.