They are different products. Please pay no attention to the marketing hype about "up to ### sq. ft."
The "Top of the Line" Orbi "50" models have the strongest radios, the best antennas, the highest speed backhaul, and the most ethernet ports. Satellites can be connected to the router using ethernet cables (if they are available).
The "20" models have fewer antennas and ethernet ports, but still do have ethernet ports on the satellites and can do backhaul over ethernet.
The "10" models are "bottom of the line". Their satellites have zero ethernet ports (none). It is impossible to connect a cheap gigabit switch to the satellites to connect things like TV's, printers, NAS systems, PC's, etc. They cannot do backhaul over ethernet. Their antennas share the 5G radio between user connections and backhaul connection.
The more money it costs, the more it does.
For a typical 4,500 sq. ft. wood and drywall construction house, one router and two satellites is probably "good enough". Placement is critical. Put an Orbi up against an outside wall, and half of the radio coverage is "outside".
Looking on Amazon tonight, an Orbi RBK13 sells for $222US. An RBK23 sells for $199US. I would pick the RBK23 over the RBK13 every time. (HOWEVER, the RB10's are "cute as hell", so many that counts for something.)
