Tell me why I should purchase the ariston heater?

I wouldn't actually. I've heard that the Ariston water heater can be quite erratic. One day it will work fine and the next day, the water will not be as hot. But that's just what I've heard personally from people who have an Ariston heater. The Joven heater at my parents place have lasted for so many years and works well. Perhaps you can consider looking into that brand too?