It should allow you to access and control the RM devices... But, with that option enabled, it's really a secondary gateway not a guest network...
If your main wifi network supports 2.4GHz, it should work without using the guest network. The fact that your main network supports both 2.4GHz and 5GHz is immaterial... A device will only connect on one frequency at a time... 5GHz capable devices will choose the 5GHz frequency, the 2.4GHz devices will choose the 2.4GHz frequencies...
I agree however see paragraph 2. Copied from Broadlink app. I have one SSID using the router's "Dual Band Selection Option". The 5G is a remnant from when I had it split. When I combined it, I kept the 5G network id so I did not have to reconnect most of the Wifi devices.
I just went through this. the broadlink will see the 2.4ghz band only. the thing you need to make sure of is that the phone/tablet you use to do the initial setup is on the same 2.4gz band as well. After set up is complete there is no reason to do this again. I disabled the 5ghz radio on my synology router just to force my phone to connect to the 2.4ghz temporarily. after setup was complete just turn the 5ghz radio back on.
Just make sure that when you turn the 5gz radio off the SSID stays the same as it was before. Mine didnt it added "_2.4ghz" to the end of the SSID name. so i just deleted that exta bit from the SSID. Your router may not do this but it probably will. It sounds messy but its really not
All i have to say is im glad I got one. I am controlling my garage mini-split and the stereo in my garage. It just WORKS and fast! and @cybrmage is always on top of any requests or fixes.
Looks like this is the only RM3 still in production, right? I'm trying to decide if I'm going to try one of these, roll some homebrew ESP8266 magic or buy another Logitech hub. These are so tiny and cheap it's hard not to try one.