We just changed the multi-surface brushes today for the first time after purchasing the machine in December. It was very easy to change them! The manual says change the multi-surface brushes every 12 months but there were places where the raised areas are absent as the picture shows. I am satisfied with the wear since there have been approx 6 events where the unit picked up a cord or string or got stuck on a rough edge. I am ordering another set. Overall Roomba is one of the absolute best work saving devices my husband has given me! It saves me hours and I am able to keep the house much cleaner. And the physical discomfort of dragging an old upright around our eclectic 1900 built two story old home is history!