My intuition as well. In fact, when looking at discharge curves for alkaline batteries and assume than any reasonable gadget will use them down to something like 1.15V (otherwise it does not work with NiMH accumulators which only have 1.22V when fully charged), I expect that you will get less than an 80% boost. That is a bit different from the claimed 500% to 800% and explains why the battery industry does not care much. (Discharge curve e.g. here: http://www.stefanv.com/electro...)
Of course a device with brain-dead power engineering that claims that batteries are dead at 1.4V would get something like an 1000% boost, but such a device is broken by design and also does not work with accumulators in the first place. Also note that if said device is an LED flashlight with step-up regulator (single-cell ones all are), it already does what this thing is claiming to do.
The break-in story adds to my impression that this is nowhere near as good as claimed.