For the money, this is a great product. 500GB mirrored (or 1TB striped, if you're feeling brave) plugged into a USB or Firewire port.
You can tell immediately when it's plugged in, though, as a fairly insistent hum fills the room. Mine got consigned to a cupboard fairly sharpish, though I guess a carpeted floor or a sheet of foam underneath would work well, too.
Performance is average for this sort of drive, but the most important thing you get with this device is a warm feeling deep down knowing your data is safe when one of the disks eventually fails.