The NFC-enabled BT540i still offers classic, phenomenal sound—refined over 56 years—but adds that Bluetooth capability. This means what? It means that for the duration of the eight-hour charge, a headphone cable isn't knocking your water all over your keyboard. (Speaking from experience here.) And if you don't charge the battery, no big deal; Koss supplies you with a standard stereo miniplug cable so you can listen wired.
As for the little jambox, it might not offer the sound of a UE Boom, but it's pocket-sized, making it invaluable for an impromptu dance party.
Ethan Wolff-Mann is an editor at Supercompressor. He has re-soldered his Porta Pros a few times over the years. Follow him on Twitter and Instagram.