I have the Fibre 2 product. Just found out that the DNS settings are LOCKED! I don't expect to pay 100% of the fee requested and get < 100% of the service. When do I get 100% service or do I have to go elsewhere?
I have no idea why that is a revelation, it is a widely publicised fact about the BT hub.
Nothing preventing you setting a different DNS server on your devices, utilising a third party router or a Raspberry pi as a DNS proxy.
If you want a router than you can change the DNS on you are free to supply your own third party router rather than use the ISP's supplied router which is adequate for the vast majority of customers who want a simple free plug and play router.