I was confused about that. It looks like it drives the chain, but then in the video after installing it or while riding it he's not pedaling.

But then when watching closely, I can see there's a cut in the video between the device being placed on the frame and him testing it and in the cut the entire bottom bracket has been replaced and the chain is now making a different path through the machine, so I assume the bottom bracket needs to also have a freewheel to make it work, plus you'll need a new chain (or to join a couple of chains) to make it fit.

The video is a bit strange: https://youtu.be/SFsnS0Yb1Bs?feature=shared&t=96 It appears to show the front sprocket spinning, but the pedals stationary.

I assume this is a "freewheel crank" https://en.wikipedia.org/wiki/Front_freewheel