Edit for posterity: In the meantime found out that indeed the HH5A physically isn't capable of Annex B. So my question is moot.
I use HH2B for ADSL. The hardware parameters are bit less impressive (not bad though) but that one is capable of both annex A and annex B (tested). So if you don't have VDSL it's an option. With VDSL it does not matter and you should be able to use HH5A anywhere.
Thanks for the recommendation, but I've got plenty routers here that either do ADSL or AC-Wifi. I wanted to have one that does both, and currently it seems that the HH5A is actually the only device that does it with LEDE.
However, I will still hang on to the HH5A. Even without ADSL it is still a very pretty and capable little machine, especially for the £7 I paid.
Yes it's amazing router for the price you can get it. I have 4 of them...
short question: have this device full LEDE support or better does the WLAN working ?
Yes. It does have full LEDE support (including 17.01.x releases), and the Wifi is working on both bands. As I said, this device is somewhat unique in that all of the components (xDSL and dual-band radio) are supported.
Is it possible to modify it then to get Annex B working? Any info on what has to be changed?