If you never have any issues with your connection and do not mind very high prices then I expect you will be happy with Zen.

The test, however, is what happens when things go wrong, and that is where Zen repeatedly fall down in my experience. For example, they mishandled a VDSL migration, leaving me without a connection for nearly a week; and I had numerous problems with their e-mail service, including when it rejected one of their own technical support e-mails as spam (!). Technical support is atrocious, and front-line staff lack even basic IT knowledge.

More generally I have experienced a refusal to accept responsibility or apologise for technical failures, alongside a willingness to lie to (or at least gaslight) customers. Perhaps this reflects a cultural problem within the company.

Zen are more than happy to withdraw services included as part of a broadband bundle without notice, compensation, or offer of an equivalent alternative.

I could go on.

Zen have now declined to the point where (for DSL services at least) they offer nothing more than any other OpenReach reseller. Given that, the only requirement is an ISP that will understand and promptly pass on any fault details and chase OpenReach on your behalf. In my experience Zen fail utterly at this and I cannot see any reason why anyone would want to become a new customer of theirs.