I have noticed you have a PRO3-VAQ and a PRO7-VAQ, how do I decide which is most suitable? General

80% of Quooker sales are of the PRO3-VAQ model. This has a capacity of 3 litres and will provide 3 litres on demand; 15 litres in the first hour of a day and then 12 litres thereafter. The PRO7-VAQ will provide 7 litres on demand; 35 litres in the first hour of a day and then 28 litres thereafter.