Add On Satellite

I think the RBS50Y is no longer produced. 

 

Can look in to this: https://community.netgear.com/t5/Orbi-WIFI-6-AX-AND-Wi-Fi-6E-AXE/Outdoor-Satellite/m-p/2129551

Netgear products can be difficult to find.  Amazon UK shows only one RBS350:

 

I found one on eBay UK, but is was an entire set and was in the 'bid' process, with no "Buy Now" price quoted.

 

If placed against an outside wall, 50% of the radio signal will broadcast outside. (In a window might be better considering how much brick is used in UK construction.)

 

Extending WiFi coverage involves one major consideration: Is seamless roaming a "deal breaker"?  The significant difference between Orbi "satellites" and ordinary "WiFi Extenders" (from any brand, including Netgear) is that satellites fully implement the 802.11 standards that allow devices to switch from one WiFi access point to another by themselves.  WiFi Extenders create a separate WiFi network.  Even if this network has WiFi credentials identical to the Orbi network (SSID/password), it is a separate network.  A device connected to the Orbi will gradually lose signal strength and quality as it gets farther from the Orbi, but will "hold onto" the Orbi until it finally just gives up and then begins to look around for a WiFi system that it recognizes.  "Aha.  Here's one!"  If simply walking out into the garden caused the Orbi signal to drop to the point that devices gave up on the Orbi almost instantly, then the user would probably notice nothing.  Otherwise, the user would complain, "why is the WiFi so SLOW???" The solution is to turn WiFi off and back on again (5 seconds).

 

Mobile devices are is why mesh systems are so popular.

 

On the other hand, if the goal is to provide WiFi to speakers, security cameras, etc. in the garden (devices that never move), then any old WiFi extender is a good solution.  There are even WiFi extenders designed to mount outdoors (weather resistant).