I just switched to them too. I’ll be interested to see how they organise their billing, they are taking out a set amount pre-paid at the start of each month which is a fair bit less than I expect my actual usage to be. It’s not clear whether I will have to pay the difference each month or if I will end up carrying the debt for a while. If they take out too much they give you 3% interest on the overpayment but I couldn’t find anything about how they deal with underpayment.