My only issue is that if I want to do a <10% to 100% calibration charge I'm going to have to pay for some peak-time electricity. That's not going to happen very often though. (I did one last night, as I came home on 8%, so that's me sorted for a few months anyway.)
From Octopus's point of view, I wonder if this is going to be counter-productive. What incentive is there for anyone to allow a charge to happen outside the normal cheap period? It's confusing, and for some people it's liable to drain their home batteries. My inclination is just to charge 11.30 to 5.30 using my Zappi's own timer, and now and again ask for a small amount as a Smart charge, starting at 11.30 and asking for the car to be ready by 5.30, to keep within Octopus's T&Cs. There's literally no benefit to using the Smart charge.