It's true that BT are good at replacing faulty equipment free of charge to those on contract, the problem is with the quality and reliability of some of their products, I got my first Smarthub a little over a year ago and I'm now on my third. OK not a big problem in the long run of things, but very frustrating at the point of failure.
hmm I'm on my third one, I kept the second from last one and managed to fix it by reseating the WiFI card in it so had a spare ( not sure it's compatible with infinity/BTTV now though ) The current one must be 5 years old and no problems.
BT upgraded me from the Home Hub 3 to the Home Hub 4 for free nearly 7 weeks ago only after 2 or 3 complains about wifi problems in the house. They gave me the Home Hub 4 as I still using the old white Openreach modem. Wifi has been mostly fine since moving to the Home hub 4. Only had wifi speed drop one evening since getting the Home Hub 4 but so far no wifi drop outs unlike what I was getting once in a while for a good few months before BT decided to upgrade me from the Home Hub 3 to the Home Hub 4.
I have always been 97%/98% happy with the BT service but there customer help via phone could be doing with being improved more in my option.
The BT Community Forums and online chat seem far better than phoning customer help service but once in a while you have no choice but to phone customer help service.
Would be interesting to know why the OP needs to use a non BT router and also why this case remains unresolved.
It would be nice to know if his problems are now sorted but at the end of the day this is a help forum and if we have helped to resolve his issues then we've achieved our goal. As my old Granny used to say, no news is good news.