So, lemme put this here and ask...do these things work for shit?
I know very little about this one. My studies of long-range projectiles for sniping has given me the knowledge that this shaping is called 'boat-tailing' and it is designed to reduce turbulence directly BEHIND the item winging through the air and thus improve performance. In this case, I assume it would be for fuel economy.
Given that it obviously has weight and thus burns somewhat MORE fuel hauling around, *and* it certainly appears that you can't open the trailer doors without removing the thing, thus being a PITA time waster at every weigh station and every dock....I can guess why I don't see many of them.
How effective are they?
...but you're right...waste of money.