The description of this connector is less clear than it should be. The four-way jack plug is connected to two four-way sockets, with each connection on the jack plug connected to both the similar connections on the flying sockets. It simply duplicates the inputs/outputs.
To be fair on the sellers (Kenable) it is fully and clearly described on their own site (as I subsequently found). At Amazon, this critical detailed information is separated from the picture and outline description by three or four pages listing alternative products. It is so lacking in prominence that I overlooked it, even when I came back to provide this comment. I was also misled by an earlier commenter who claimed that he had successfully used it to combine headphone and mic connections (I now see that Amazon has not verified that this is the product he purchased).
This is DEFINITELY NOT equivalent to the type of splitter that is normally required for matching headphones and microphone to a four-way socket as now used on some laptop PCs. This application requires a part such as http://www.amazon.co.uk/Startech-com-3-5mm-Headset-Splitter-Adapter/dp/B004SP0WAQ/ref=pd_sim_ce_1
The cable itself does the job it is actually specified for perfectly well, and it is well constructed. One star removed because of poor description at Amazon.