Hi Mak
check the fuel cost rate from normal payments to the online payments, scottish power provided me with a price booklet when i joined and that gives you the comparison for all the different ways off paying and running account. it was a low rate for running it on line , also you get to keep your reading upto date and you get the ability of seeing what is peak and drops in energy level use.
this is found by my own trial with the accounts, i been with scottish power for about 3 years on and off line with moving address.
Jeff