USB thumb drives are generally very small and portable. Old NES cartridges? Less so. But hey, this custom NES USB port and accompanying USB drive cartridge have style.
Essentially, the old NES has been converted into the world's least convenient USB drive. And a cartridge has been retrofitted with a USB drive to plug into it. Sure, you'll get the satisfaction of popping an NES cartridge in whenever you need to transfer data, but good luck fitting that cart in your jeans pocket.