This seems to have worked quite well as can be seen below. Here are the different synchronisation speeds.
Without Annex M:
With Annex M:
That’s quite a difference especially if the upload speeds are important.
I’ve already been told that my video over Skype is better and also noticed less problems with VoIP although the increase from 320 kbs I had with Telefónica is sufficient to avoid many of the dropouts I had experienced earlier.
Here is the Jazztel configuration I’m using:
Hopefully if you are considering using this router this information may be helpful to you.