Thks both Eddy and Stardust for answering on my behalf.
This unit is definitely not suitable to support livestock for a 5ft tank, regardless whether be it marine or freshwater.
However similarly, if you intend to use it as a form of chemical filter for a 5ft tank; e.g. by placing only carbon in the canister, I believe it could perform its duty fairly.
Hence, its never "way out of line", but depends how you apply it.
Well I would say this unit is suitable for tank size below 30gals, or about 115liters. Of course that also depends on the no. of livestocks ones has inside the tank.
Thanks and hope that helps.