Wiping a flash drive is not the same as wiping a disk.

When you overwrite on a disk, the contents of a sector are replaced. On flash, the controller remaps the sectors, and without taking the thing apart and bypassing the controller, you cannot know whether private information remains.

Also, a secure erase will shorten the lifetime of the flash memory. Just erase it through Explorer (remember to empty the trash) and reuse it. Or destroy it. There is no real middle ground.