I can't phathom a reason to build one this big. Other than to say so. I have made pretty big units and never an issue or efficiency problem.
There is no claim being made that this is more efficient, the only reason why its long is because the reactor is being ran horizontal instead of vertical. Plus i had to buy the 4" pvc at a minimal length, so i cut one foot off it and built it to fit behind the stand. We enjoy the equipment aspect of the hobby just as much as the stuff inside the tank