It is a flashcard. It lets you load copies of games onto a SD card and the Switch will read them as official cartridges. The site mentions that its only for backups of your own purchased games, but most people buy them for piracy.
That's very interesting, thanks, I didn't realize you could load downloaded games onto a Switch like that. I imagined they have some sort of hardware verification.
Overall this is very interesting. The game switching mechanism seems a bit fiddly though and I hope there will be a version with a button.
I wouldn't be surprised though if the whole operation will be shut down completely by Nintendo so it might not be a bad idea to buy one.
The same thing happened with the DragonInjector (small payload runner for jailbroken switches that fits in the cartridge slot).
