Using NBR750 as a satellite on a RBK752 system

Some brands of mesh WiFi are designed where each unit can act as the base router or as one of the satellites that form the mesh.  Netgear Orbi is not designed that way.  Amazon is showing RBS750 satellites for sale at $200.  eBay has listing for used RBS750 starting at about $100.

There are a number of issues to be addressed:

• Network Connection.  Yes, the surplus RBR750 can be put into Access Point (AP) mode and used to create a separate WiFi network for the garden area.  But, unlike satellites which can be connected either using the built-in WiFi network or with an Ethernet cable, the RBR750 must be connected to the primary network with an Ethernet cable.  That connection might be awkward or expensive to accomplish.
  Typical WiFi Extenders, on the other hand, are designed to connect to the primary WiFi network using WiFi.
• Getting the signal outside.  Depending on the building construction, a WiFi access point placed indoors may not push a strong signal as far as you need.
• Weather.  Netgear Orbi systems are designed for interior use. They are not rated for outdoor use, either in terms of temperature, humidity, or inclement weather.  One solution for this is to place the Orbi unit inside the house, but either (a) (literally) next to the exterior wall, or (b) sitting in a window (and not one of those triple pane, metallic film, windows.
  There are WiFi Extenders that are designed to be placed outdoors.
• Power.   If the unit is indoors, providing electrical power may be trivial.  Outdoors can be a totally different situation.  Once again, Outdoor rated WiFi Extenders are often powered using Power over Ethernet (PoE).  Whereas running a 120v. line through an exterior wall involves the electrical code (i.e. "can't do that without an electrician"), PoE cable requires a 1/2" hole that can be weather sealed with little effort.
• Roaming.  If this mower will be the only device in the garden that will require a network connection, then any brand of WiFi Extender (or that RBR750 in AP mode) will work fine.  However, if there will be other mobile devices that go between the garden and the main house,  only a true satellite will will provide seamless roaming "in and out".

Thus, if there is a handy window and it is easy to get an Ethernet cable connection, that surplus RBR750 would be a great solution.  If not, it might be time to look into an outdoor rated WiFi Extender that will connect to the primary network over WiFi and can be powered with low-voltage cable .