All of our Classic Light Strings (vinyl only) have integrated clips on each socket.
Our Deluxe Light Strings (fabric wrapped vinyl) are made with the only available modern sockets for this type of light string, and they do not offer clips.
In our own experience with them, we rarely find the need for a socket clip as the light strings are very flexible and both drape and lay on greenery very well.
If a socket needs more precise placement, you can easily twist the two wires apart near the socket and place it over a branch tip to secure, or use a simple non-metallic twist-tie or zip tie.