Hi Meldrew and Catastrophica,
I have the One Account, choosing it to pay my mortgage after considering the options. The flexibility of the whole thing does make it very easy and I have paid my mortgage off in a few years. If you are good at paying in your salary and leaving it there, you will see the "debt" steadily decreasing. Interest is calcluated daily on the balance, so the more you can leave in the lower the interest charged. I think this is a great product for those people who are fairly good with their spending and keen to pay off the mortgage sooner than usual (and therefore save a lot in the long run). I'd be happy to answer more specific questions if they arise. Another incentive of course is the £125 cash back offer if recommended by an account holder.