Did this get solved? I have just recieved my R3 today and have fibre BT and a smart hub but I saw on BT website if you have fibre you don't need to use the smart hub at all when connecting your own router you can plug the cable straight from the ONT into the WAN port on the R3, so I will try this later when I set it up and update with my results.
I assume this will then fully rely on the R3 for security and stuff then? Or will it be the same as if it was dmz or bridge mode anyways? @Netduma Fraser