Lee Rosenbaum takes the electronic Concert Companion for a spin. “The constant flitting between commentary, video and the live performers, the glitchy image quality and the need to reboot after several crashes put me in a state of nervous agitation rather than rapt absorption. CoCo’s chief drawback, though, is that words can never adequately translate music. Background reading is helpful, either before or after a concert. But the best way to appreciate a live performance is to switch off all electronic devices and simply employ your ears.”