Made in the USA is refreshing to see! The insulation piercing feature allowed socket placement along either a 2-wire zip cord, or THW strung parallel. IMHO a 'decorative' use item.
I remember years ago, every corner used-car lot had those lights strung around its perimeter, usually on twisted two conductor cabling. They were the standard Edison socket version. You still see a lot of similar "temporary" string lighting using these sockets at Christmas tree stands this time of year.
Eagle used to make a version of these (at least an Edison base version) that was pretty cool. They had a quarter-turn "T" shaped knob that clicked into the closed position and was reusable. The little ones are also available with a metal mounting bracket and were often used in furniture. I have a china hutch that has several of them looped with zip cord in my dining room. It is only a few years old.
I had some of those candelabra base sockets around a makeup mirror in a cabinet I built for my daughter. We put globe bulbs in them for that Hollywood look.