I really liked the concept of this kettle, and found it very easy to use. As previously mentioned, the guide measurements are for cups rather than mugs - I found that 1.5 cups is about the same as a mug.
On the downside, I have had my kettle around 9 months and it has already started leaking from the "boil" compartment. Consequently, I have to stand it on a towel every time I want a cuppa - not ideal! Means that my eco-kettle really isn't anymore as it is losing water everytime I use it, plus I now have extra washing to do with all the towels... Possibly just unlucky and got a faulty model, but please be wary.
Great concept, but definitely needs a little more thought on the design front.