There are two major reasons to swap out the headphones that came packaged with your MP3 player. The first is sound quality, and the second is fit. The two are not mutually exclusive, but you may place emphasis on one over the other depending on your device usage. If you mainly use your MP3 player at the gym, getting a pair of headphones that both fit securely and offer some sweat resistance is key. The $40 Nike Aero Sport Headphones certainly fit the bill there, and although music doesn't sound great through this set, the sleek and sweatproof design may appeal to some.