external drives are hit or miss, i have used two pre-built/manufactured externals and have worked OKAY, but not something id generally keep any necessary data on.
So i go with a DIY approach, purchase an external enclosure with FW400/FW800 with a internal SATA connection and pick up trusted and generally cheaper internal drives and there you go!
that way if the external manufactured drive you purcahse goes kaput, well aside from breaking it apart to get the drive out if youre lucky.
atleast with the DIY you can buy as many cheap internal drives as you want, and use them whenever you want, one specifically for time machine? go for it, well you need to clone your OS, remove the TM drive slap in the OS back up bam, after that need to make a specific drive for movies/music/media etc? slap that in, after thats taken care of remove that and slap the ol time machine drive back in and continue where you left off.
hehe
😎