Basic just-good-enough clip/third hand to help you change filament on an Ender 3 with one hand. Slip the large open rectangular end over the extruder tension arm, squeeze the arm to release grip on the filament, then slip the little flag into the open arm on the other side of the extruder. Allows you to dedicate all your attention to getting the filament loaded.
Once you've loaded new filament, squeeze the extruder arms again and slip this little clip off.
This tiny part takes less than 10 minutes to print.