People using this hardware (to hack into the Switch) is a removal of a software protection. Which by itself is illegal in the EU (where I live). Selling of these devices (to hack the Switch) is also illegal. (At least here in the Netherlands, but it should count in the rest of the EU as well.. see Nintendo versus R4DS cards a few years back)
Distribution / download / use of a game you don't own is illegal. Everywhere. Distribution of a game you own (license) is illegal as well, since you actually don't own the game. You own a license to play the game. Download of the game is only legal if it's a free update from the Nintendo server, a purchase from the eShop, or DLC (purchased from the eShop).
Downloading a game you already own the card of (download from the internet) is ALSO illegal.
So ONLY making a backup of your owned gamecard is legal. HOWEVER you still need to break both the protection of the Switch AND of the gamecard. Which is illegal in the EU.
So yes. ANY use of this device is illegal.
And on a personal note: I like to add why I am 100% against ANY form of Piracy or console hacking. Third party publishers will refuse to make games for the Switch if the pirates will just steal / pirate the games. This is what happened to the DS, 3DS and Wii. (Wii U had other problems)
Also I work as a software developer (not games) and I like being paid for my work. And this is only possible if people buy the software. I can imagine developers at Nintendo & other studios feeling the same about this.