Hello! Using the BT Hub 3A that was given to me for free, I have successfully downgraded my firmware so that it was unlocked, and used the SMB solderless procedure to get an openRG root - even managed to enable the SSH login that had been eluding many people (not that it was needed).
I followed the installation procedure, installed a ubootenv-tftpboot with an openwrt ramdisk, then finally successfully flashed OpenWrt onto it using sysupgrade using the lantiq v19.07.8 squashfs image and the backed up wireless configuration data that I saved as eeprom.bin.
problem 
So, my problem is that I can only see one radio when I go to network->wireless - there is no other listed, even though I know that the hardware does have 2.4Ghz and 5Ghz wifi capabilities... its not greyed out, or disabled, it's not even there 
- is there any way I can get the second radio to even appear?
I'm taking a punt that the problem is because my backed up wireless configuration, that was saved from when it still had the factory firmware on it, only had 2.4Ghz enabled. I just did a google search, and (not read the full thread, just saw the title) it appears that although 5Ghz hardware is there, it's not enabled by default, and there is an upgrade needed to turn it on. So do I need to roll back to the BT firmware in order to do this upgrade,. to save the wireless config data, or can I get this working without removing openwrt?
Although I am confident diddling around with firmware and hardware (plethora of experience, I'm a software engineer, semi-retired) I have zero openwrt experience other than the above description 
so I have no idea of its capabilities other than what documentation I have read so far...
Thanks in advance!
- the guy upgraded his HH3 by unplugging it and plugging in a Smart Hub 3... D'OH!