Playing devils advocate here.
So what's stopping you installing an Octopus approved EV wallbox (charger) for lets say £500 even though you don't own an EV to then make full use of the Octopus 7.5p rate to charge your house batteries like John does, in order to run the house all day.
You could even rent out your unused charger to EV's at premium day rates
Even if you only took 6kWh a night at 7.5p rate instead of the Flux night rate, your outlay (roi) is less than 2yrs. In practice it would work out considerably less than that.