If you're asking about the portable FreeAgent, called the FreeAgent Go, I recommend it highly. I've bought four of them (the 250GB USB-only version) for my family, and been delighted. One is the everyday bootable-clone backup of my MBP's internal drive that I carry with me everywhere. It's reliable, needs no external power supply, boots my MBP promptly without fuss when asked to do so, and is almost silent. Comes with a reasonably well padded slipcase and very small, handy USB cable that fits in a little elastic pocket on the outside of the case. Handsomely styled, very compact and portable, and very inexpensive: $70 on sale at Costco.
There's a "Mac version" with a FireWire port, too, but for the use I'm making of mine I don't need to pay $30 more for FireWire. I just trashed the Windoze-only software that was preinstalled on it, partitioned and formatted it in Disk Utility, and put it to work. Once I'd seen how satisfactory mine was, I bought them for my wife and two grown kids too.
They are 5400 RPM drives, not 7200 RPM, in case that matters to you.