*note it will drain your battery wayyy quicker than an SD, I was looking at 2-3 hours on full battery while powering the drive instead of 9-10 with SD card, When I use mine I just copy the needed files (usually videos) off it to SD and then unplug.
Some drives (such as, in my personal experience, LaCie ones) will try to draw too much power, won't work, and will cause the Pandora's screen to fluctuate in the same way as a CRT with a magnet being held against it would. Just making a note of it.