2 years of problems. Lovely staff who all promise to help but they can't fix the issues which started when they tried to take over my neighbour's broadband instead of mine, then *insisted* I had a new line put in despite there being nothing wrong with the line I had and ever since then, nothing but drop outs, speeds less than 1Mbps. Every time you phone tech' support, they say "it's your router that's at fault". Here I am, 2 years and 6 routers later and I'm migrating to another provider and the minute they got notified, I've had no internet.
Phoned tech support, they were very busy and promised to call me back twice and never did.
I'm only online now because I bought a day's worth of internet from BTfon.
I could never recommend Zen. They are more expensive than other providers, but the service is dreadful.