Although the original IRobot Roomba was the first commercially successful robot vacuum, it was not the first commercially available. The Electrolux Trilobite was released one year earlier in 2001, and while it was more advanced than the Roomba, the Roombas much lower price allowed it to win out.
One of the main differences was the Trilobite mainly relied on ultrasonic sensors to navigate, with bumper sensors only for if the sensors missed an object. The Roomba on the other hand navigated mainly with the bump sensors on the front, while also using basic ir sensors to detect cliffs and perform basic wall following.