I'm running the Tomato firmware on my Asus which is really good with many features.
There have been issues previously that have indicated that no matter what DNS provider you choose, BTs transparent proxy can override this.
You can try changing your DNS and see if you can reach a site blocked by the Gov. for example.
If you want to really be sure where your DNS is going these alternative firmwares support DNScrypt which currently cannot be intercepted.
When I choose disconnect in my HH5 options, then I do not get any options to choose AUTO vs MANUAL DNS? However, it will automatically choose BT DNS upon reconnection?
Is it not possible to set DNS manually?
could BT consider adding this option for the home version as your DNS servers are frequently unreliable nation wide??