One interesting use I can think of is to simply carry one around in case you get arrested by the police.
Supposedly police require a warrant to search your personal papers such as your cell phone, so this shouldn't be much different. If they take the USB drive over to the cruiser and plug it in "just to see" then this will fry their system.
You can even tell the officer not to plug the device in, that it's not a thumb drive, and that there's no information on it.
It would probably work at airports as well.
I really don't see a downside to this.
Well, let's start with the fact that police equipment are paid with your taxe, which basically mean you're burning your own money.
Beside, I don't get why so many people have so much hate again the police. Yeah there's a bunch of them that are asshole, but asshole exist in every profession. It's just that it's more of a problem if it's a police officer (or a politician) instead of the garbage boy.