Before getting bogged down in the question of what this is, consider the more important issue of "why" this is. There are certain things in life worth pondering. Whatever happened to your socks is not one of them. "Why not?" comes the plaintive cry from exasperated parents taken to feeling miserable about their lonely bag of single socks. We agree that this is a great idea, as having a handle on socks as they roll around the washing machine means that hours aren't spent unmixing and rematching. And poor little socks don't go through life thinking they are on the single shelf.
But let's put as much thought into it as the manufacturers have. Once these little feet are attached to socks, you then have to detach them in order to wear them and re-attach them to wash. Hardly a time saver, as the whole manoeuvre involves a complicated push through mechanism, plus finding the matching socks in the first place.