I have found similar items in the key-chain section of my local hardware store and discount stores for around a buck. Some come with nylon twine inside and some with steel cable I buy the steel. I ripped the hook, pin, clip off the back of one and fit it into my Altoids tin. The one I found has about 2 yards of cable and is about the same size as a photon light. The spring is decently strong. I figure it will be a decent self setting snare at least, if not useful as a trigger spring for larger snares built with my snare wire. Similar use in fishing to the YoYo fishing reel. The only thing missing is the triggering device and that can be improvised fairly easily in the field with small twigs and the Xacto balde in the kit.
Good items to have around. I have even used one as a clothes line in the back of my jeep cherokee. Stretches taught between the back-seat hand grips and holds nicely.