Using Orbi Router in Access Point (AP) Mode

I have connected my Orbi Router RBR50 to my existing Plusnet Hub One router with an Ethernet cable, turned off the Plusnet WiFi signal and and set the Orbi router to AP Mode. All great. 

Looking at the list of detected WiFi networks I can see both the Orbi and the Plusnet (even though the Plusnet WiFi signal is definitely turned off). Which network should I use for all my devices - the Orbi network or the Plusnet network or doesn't it matter ??