| Looks like a gimmick intended to have you replacing your substrate every week or two. If you let normal gravel establish bacteria it also removes ammonia. This product seems to work like ammo chips taking the ammonia away from the bacteria that would develop if it wasn't there. If you leave it in it has to exhaust then you're right back where you started needing to either replace the substrate which I'm sure is great for Penn Plax's bottom line or waiting for the exhausted substrate to cycle.
You could accomplish the same thing dumping regular ammo chips in with your gravel but probably cheaper. | 
