Well, we had a Quooker as a "luxury item" in our kitchen refit way back in 2008....& what a great device!
Morning tea ready "instantly". Safe to use (twist and push tap), we love it!
I measured the energy used with a meter - the kettle before, then the Quooker, and in our kitchen we found the Quooker was around 15-25% more energy efficient. The range is because we measured the kettle over 30 days in total, but for different periods (7 days, 16 days, then 7 days again) - overall it looked to me like the Quooker was around 21% more energy efficient.
To be brutally honest, we were not desparately scientific about it - we didn't make absolutely certain we had the same numbers of cups of tea, etc...it was more a "quick test", really to find out whether our decision was better or worse for our energy cost (& ergo, the environment!).
You could never justify it on raw economic grounds.....it is simply to expensive up front (although we paid way less than the price in this article!).....it is a luxury item.....but one we have never regretted lashing out on!
I guess we should think about replacing the filter now....but it still makes great tea, so maybe I'll leave it another year or six.....