"Discovery" really doesn't matter much for most users, as it's encrypted,
preferably with both a passphrase and multiple keyfiles, depending on the
extent of the security desired. It's really little more than "security
through obscurity" which of course only adds a marginal degree of
protection from casual explorers who might just see the extra partition as
having been formatted in some incompatible (with their system) filesystem.
Overwriting shouldn't matter either, as anyone who is concerned enough to
protect their data with decent encryption should also have proper backups.
Personally, I encrypt all of my USB sticks, just because I never know
what I might want to store on there temporarily. I don't often use the
partitioning scheme mentioned in my previous post; usually a standard
encrypted container will suffice, as it simplifies the process a bit and
makes backup a wee bit easier.