After connecting, you can simply switch the network back to 2.4 and 5GHz.
This is because your phone needs to be on the same Wi-Fi frequency as your Duux device for the connection process to start. This communication is not much more than the login details for your router. Once your Duux device has the login details, it will log onto the network and communication between phone and device is no longer necessary.

Note: The above explanation applies only to Beam, Beam Mini, Blizzard, Whisper Flex (Serial numbers starting with 21CF or lower), Bora, Threesixty, Tube and Bright (Serial numbers ending with: DXPU06: 0500001 - 0501800 & DXPU07: 0500001 - 0501600)