I dont know why its appealing, but it certainly is. The ball speaker can be attached to any MP3 player or music player thanks to its normal 3.5 mm stereo audio connector. Its small and portable and more than loud enough I am assured. The person in the snap is hanging it around his neck, but I doubt thats ever going to pick up.
If you insist that your co-travellers listen to your choice of music on the iPod then make sure you get it. At 17$ a pop you wont be too hurt if an enraged commuter throws it out the window.