I work very part time at a feed store. The company rep for crystalyx brought one of the biobarrels by for us to display. After looking at it and listening to him discuss the pro's and con's, I think I prefer the metal tub for my situation because I have few cows and they are all right at the house.
The plus would be for the guy's that lease a lot of different places. It's quite convenient to drop of the tubs and forget about it. You don't have to go all around picking up empty tubs to return to your favorite feed store.