I wouldn't use quantum then, they would be useless without 24hr supply.
Why do they want to change the storage heaters?
If they are just looking old or are not automatic then any replacement automatic storage heaters would be OK.
If they are looking for more flexibility in their heating then you would have to go for installing a 24hr supply and using quantum, combination storage heaters or just panel heaters which would be just about as effective if they stop the E7 tariff
.
I have not really cottoned on to the advantage of quantum and how it will really save you money, as far as I can see it is just a combination storage heater with automatic controls to waste money when you did not actually need the heat. Convenient and easier to use than most others but not cheaper, despite their claims. However I haven't fitted one so I could be very wrong.