I agree that as far as the energy goes you would still use the same amount of energy to raise water temperature up 30-45 degree, even though you may use a different approach. The advantage of the technology, though, is how you could heat the water mass as a whole, instead of just the heating surface. It is more efficient way to heat your object.
A normal microwave device would have 65% efficiency meaning that 1 kw applied would transfer only 0.65 kw to the water. Then the other 0.35 kw would mostly (not all) be loss as heat. WDRP claimed that their strategy was to reuse that wasted heat and reapplied it to the water, which is a rather simple concept using in many industry. That was how they said that they could be 20-25% more efficient than current microwave heating setup.