It means the StartMeStick can be very effective at protecting your privacy from mass surveillance, e.g. the systems used by companies and governments to collect then process our online activities en masse in order to drive our engagement and their profits.
It’s not private (or secure) from specific/dedicated attacks from skilled hackers against an individual, e.g. if you’re a government spy trying to hide your trail online, you should probably invest in something "bigger" than a StartMeStick.