Some use shed loads of Adblue. Some use hardly any. My X350 drinks it. Some customers go between services without topping up. I have no idea why this happens. I just know its a awful, flawed system and should be scrapped. It simply doesn't work properly in the environment that its in.
On my soap box....
Adblue is on cars to reduce emissions. But, the systems fail so often that it doesn't seem very efficient at all. Parts have to be produced in the first place and then again, and then again. Eventually a replacement part will arrive at my workshop in Horndean after traveling many miles to get here.