Just got my bill. Average savings this week: 4%. My savings this week: 30%.
I was thinking about their reported "savings" when I looked over my bill yesterday; I too noted the average savings of 4%, but my "costings" percentage figure was noticeable by its absence!
I think the more honest approach would be for Flick to be up-front about the additional cost, eg "Your bill this week was 12% higher than it would have been with your previous provider" or words to that effect. Sticking some preamble on those bills where the cost was higher to explain this (like my bill has) doesn't quantify the extent of damage. Yes, this can be calculated by the customer, but it just should be provided on the bill I reckon.