When FTTP/H became available in my area I took a risk and went with BT as they were the only service provider offering 1Gbps. I had hoped that as a business they may have improved, alas I was sorely disappointed: Their router is not fit for a Gigabit (900Mbps as BT call it) service, it's the same hub used for VDSL so you instantly lose an ethernet port. As for the customer service, the people clearly try but there still seems to be the attitude that "We're the incumbent we can do as we please, if you don't like it go elsewhere (once you're no longer locked in).. Avoid at ALL costs. As for the speed, I'm lucky if I get over 700Mbps but as that's above their speed guarantee they don't seem to care! Honestly if I could give them zero I would.
*Update* Following a lot of testing of different config, I have found that with BT's hub connected to the ONT, the wifi off and my router in Access Point mode I hit an average of 800Mbps however when I'm using my router to establish the connection I am lucky to get more than 500Mbps. All the same cables are used in both setups only with the addition of another CAT6a cable from the ONT to the BT Hub. Quite honestly I am beyond furious and will go back to Virgin Media (yes I can't believe I'm saying that) as soon as the contract is over.