How could CityFibre have anything to do with downtime on another physical network -even if they are using the ducts and poles?

Big boots and rope burns.

At 1:00 am? For 15 minutes downtime?

My experience of Zen has been absolutely first-class.

I moved from Plusnet when my contract ended as FTTP was scheduled to come to our area, and Plusnet couldn't offer it.

I spent 14 months on ADSL before switching to FTTP but even then latency was instantly halved.
Calls to Customer Service (mainly to migrate domain names as they were cheaper than 123-reg) was met by people with thorough technical know-how, not just working from a script.

Migration from ADSL to FTTP this summer was seamless and simple, I kept the same static IP which saved me a lot of messing about on my network server and since then I've had rock solid 100/20 meg connection (actually 10% more most of the time) with 6-7ms latency. There has only been 10 minutes downtime in the small hours one morning.

I've only been a customer for 18 months, but are they any good? Yes they are! Slightly more expensive than most, but worth it.