I've followed the instructions and managed to get lede-lantiq-bthomehubv5a_ram-u-boot.asc uploaded to device.
After that it boots up and I get the BTHOMEHUBV5A prompt.
I'm unable to ping 192.168.1.1 however. My laptop is correclty setup. If I rebooted the HH5 again I can access it via 192.168.1.254 (the default) so network/cables are good.
However with the uboot image loaded I cannot tftp put or ping 192.168.1.1 (also tried 192.168.1.254)
What am I missing? I've tried connecting to every yellow port. Makes no difference.
Update: Rereading the latest PDF did the trick 
https://openwrt.ebilan.co.uk/viewtopic.php?f=7&t=145
All I had to do was run tftpboot .... on the HH5