The problem with walking in traditional downhill ski boots is the fact that their soles are flat and rigid – your feet can’t roll on and off of the ground, as they would with regular ol’ shoes. While there are already other attachments that can be used to make ski boots easier to walk in, these usually have to be taken off while skiing.
Zuke, on the other hand, is designed to stay on the boots full-time. A rubber sole piece in the front stays forward when the boots are being used for walking, and is then pulled back into the middle when clipping into the ski bindings. According to Shirion, the mechanism is highly resistant to freezing up.