The IRobot Roomba S9 is the oddest Roomba ever produced. It is the only IRobot model with a D shape instead of the circular shape every other Roomba has been. Unfortunately due to the odd shape, this model has a lot of parts only for the S9 itself, meaning that despite it only being one generation discontinued, it has the worst support of any of their robots parts wise (IRobot has already said they have stopped producing certain parts for it like wheel modules).