At $50+/- shipped, the Auralex Gramma or Subdude cost a fraction of what some folks have spent on their subs and a miniscule fraction of the complete setup.
To all the folks on the fence, just get one and try it. If you dont perceive a change worth the money, simply return it or sell it on AH classifieds. I am sure it will get picked up pretty quickly.
I have one and recomment it.