I've got two of these. One is used by my daughter to plug her headphones into a guitar amp, the other is used by my wife to plug her headphones into an electric piano. The connection between the adapter and the headphone plug is nice and solid, as is the connection into the phone sockets on the amp and piano (and my old hifi system when I borrow one of these to use my headphones). There is absolutely no hiss generated and the sound quality is excellent.
I can recommend these these to anyone who wants to take a standard set of modern headphones with the small 3.5mm plug and use them in the old 1/4 inch sockets.