RBK40 satellite extension

You can add any Orbi satellite to your system, including RBS20, RBW30, RBS40, RBS50.  Many are available on the used market, such as eBay.  You cannot add any model of router, i.e. any model RBR. Another alternative is to install the less newer, expensive "10 series" product.  This is pretty clearly aimed to compete directlly with things like Google Mesh.  The BIG limitations on this new product are that it has only one ethernet jack (on the router) to allow connection of one device or a switch.  None of the satellites have ethernet jacks, so there is no way to wire any devices directly to satellites.  Not a huge problem for many customers as long as "that works for you."