You asked
Is the 7artisans 6mm f 2 worth buying used?
Here is what the site says about that.
From 7Artisans 6mm f/2: 7Artisans 6mm f/2: A prime lens by 7Artisans for APS-C cameras, 6mm f/2. Specs - Maker: 7Artisans - Focal length: 6mm (prime) - Maximum aperture: f/2 - Made for: APS-C sensors - Mounts: Sony E, Fujifilm X, Nikon Z, Canon RF, Micro Four Thirds - Stabilised: no - Autofocus: no, manual focus What it frames like - On APS-C (Sony E, Fujifilm X, Nikon Z): like 9mm on full frame; f/2 gives about ...
From Buying used: Buying used: Cameras and lenses are built to last, and many photographers upgrade often. That makes the used market one of the best ways to afford good gear. A body that's one or two generations old is often most of the camera for a fraction of the price.
Quoted from this site's pages.