A hook to clean the molten plastic as it comes out of the hot end.

Used for filament changes and oozing operations. 

It keeps your fingers away from the hot metal and plastic.

Use your default PLA settings. It uses very little plastic and is designed to be disposable, as you can see in the image, at some point it will become too used and need replacing.

It's a tool and so will get worn out, or over clogged.

I use this when loading filament into my Prusa XL. When loaded, the nozzle will ooze, so when sending the head back to park, I have the hook remove any ooze that has come out of the nozzle after loading the filament. This is why it looks a mess, as the little bits of ooze stick to the hook. It makes the bed levelling more accurate, as there is no extruded material between the nozzle and the bed.