If it's fast, you'll end up with an extremely hot metal rod at the end of the cooking process, which you have to wash if you're heating anything other than water, and which will burn milk, soup, etc. Plus, you can't use it with metal containers, so a stainless-steel insulated travel mug is right out, unless you want to drink your tea with an oven mitt.

Plus, there's no mention of how much of a household's energy budget is spent heating water. I'm guessing "not very much," so energy savings are a red herring. $120 spent on LED lights or insulation around your hot water heater will probably save a lot more.

To make a single cup of hot water, it's much easier to: (1) microwave it; (2) stick in an immersion heater; or (3) pour a cup's worth into your kettle, turn it on, then pour the result back into your cup.

EDIT: Relevant, more detailed analysis: http://physics.ucsd.edu/do-the-math/2012/05/burning-desire-f...