Eventually it cleans every part of the room—but the anti-Roomba crowd claims that it does so unevenly, going over some parts of a room many times while cleaning other spots just once. A more systematic approach could yield greater efficiency: If a robot cleaned each part of the floor just once, it would have a lot more battery power to clean more forcefully and could clean more quickly, to boot.
That's the theory behind both the Neato and the Mint. "We clean your floor the way a Zamboni would, or the way you would," says Max Safai, the CEO of Neato Robotics. The Neato uses several different sensors to create an internal map of a room. Based on this map, it will first clean the room's perimeter before going back and forth within the perimeter in a systematic way.
See videos of both the Neato and the Mint in action at Slate. Link