It’s exactly as described, an official Nintendo USB adapter that allows you to use Gamecube controllers on Switch and Smash Bros Wii U. Controllers are completely responsive, rumble works. The only thing is that in a lot of Switch games, it doesn’t work that well because of the lack of a second bumper and clickable sticks.
https://www.amazon.com/GameCube-Controller-Adapter-Nintendo-Switch/dp/B07DJX3ZR8

