All of the "original" 802.11ac Orbi satellites will work:
RBS50
RBS40
RBW30
RBS20
RBS40V (voice)
RBS50Y (outdoor)
None of the "AX", "Pro", or "10" series products will sync with the RBR50 router as satellites.
There are hundreds of "WiFi Extender" products that can be used to expand the coverage area, but they create separate WiFi networks and devices will not "roam" between the Orbi network and the extender. In some cases, this is not a problem. If the need is to connect a device that does not move, but is too far away from the closest Orbi unit to get a good connection, then a WiFi extender can allow that device to connect to WiFi. (irrigation controller, garage door opener, security camera, etc.)
