Our old robot would bang its way around the house in a random pattern. This one goes back and forth over the area, stepping over each time. The old robot was always stuck, and hard to clean. The new robot just does the job. Handles most obstacles  but rarely gets stuck. 
Our Great Pyrenees dogs shed a LOT and this robot does a pretty good job handling it all. It does build up on the brush and on the brush axle requiring constant attention
 This constant attention is the Only reason for less than a 5 star rating.