Energy-efficient external hard drives? Hyped?

[Durbrow]

Hi. I need to buy a backup drive, preferably one suitable for TimeMachine, and I checked out energy-efficient drives. Do you think any PORTABLE firewired-powered drive would be energy efficient compared to this USB2 Kanguru Drive at amazon?

http://www.amazon.com/dp/B000XJ77J0?smid=A2YLYLTN75J8LR&tag=yahoo-ce-20&linkCode=asn

Thanks for any comments!