Magnetic Media - Hard Drive Eraser Wand

This looks pretty interesting although pricey:
Datastroyer Disk Erasing Wand
I have seen strong rare earth magnets (neodymium) erase credit card mag stripes (on the tv show MythBusters).
But can they really erase all the data from the many platters on a hard drive just by passing it over the outside of the drive?
Wouldn't the platters near the point of contact be totally erased (would they?) and the inner platters be only partially affected?
Is recovery after such a strong magnetic exposure still possible?

Here's an interesting neodymium link:
http://amasci.com/neodemo.html