yes we had them until recently.
Like you, there really just wasn't any choice. It's the decision of the management company. As far as I know, they did the billing etc, but the management company somehow set the rates and organise the maintenance. When we were with switch2, the rates were really high, but they are lower now that we are with a new company - it's not clear why that is, though, as I don't think it was them that set the rates.
We have had various problems with the heating system and lack of maintenance from the start, but I don't think it was Switch2's fault.
So while the experience under Switch2 was fairly rubbish, I don't think it was particuarly to do with them, and more to do with this particular type of heating system, which is not without issues. Apparently more eco-friendly, though, but not necessarily cheaper for residents and not without maintenance issues.
However Switch2 were fine to deal with in terms of billing and customer service and so on, always answered emails fairly promptly and adjusted bills and direct debits fairly.
There's basically no choice though. You either accept them or you don't live there. You can press the management company to change suppliers or change rates or something though once you're in.