I can comment on my experience with OVO. I was previously with Scottish & Southern on Economy 10 and had one of their dual reading meters installed. I have now swapped to OVO (because of price and customer service issues) and they treat my Economy 10 as if it is Economy 7. Which means that I get 10 hours of off-peak electricity, as before, but are charged by them as if it is Economy 7. There’s no other way that they could do this as it would involve installing a new meter, which they won’t do. They don’t have access to the inner workings of the old S&S meter and are content to stay with the S&S scheduling of peak vs off peak hours.