The RBK53 is a packaged kit including an RBR50 router and two RBS50 satellites. The RBK53S from Costco is described as "Orbi AC3000 Tri-band WiFi System with Advanced Cyber Threat Protection". I have this same system from Costco, purchased in March, but my RBR50 router is v1 with the USB port. They are probably shipping RBR50v2 exclusively now, which does not have the USB port on the router.
From what I can tell, RBK53 and RBK53S are the same, as both include trial versions of Armor and Circle. I initially enabled Armor, but I was not impressed with it and uninstalled it. It was more of an annoyance to me to have Armor ping me with alerts every time a device attached to the WiFi, and its device naming feature does not work with the routers device naming, so to name a device you have to do it twice; once on the router and once in Armor. Plus it blocked many legitimate web sites that I needed to visit, including online news sources.
