The Russian rocket engines are also a little bit more efficient due to the design. Mostly they didnt know that the Americans believed that something was impossible - so they just went and tried it.
As for it being a better option Im not sure. They have to think carefully about it.
I think that the US defense department think it is a better option than being dependent of oilproducing counttries.
When producing ethanol one produces carbondioxide with this method you use the carbondioxide as well !!! It burns cleaner and the process is clean.