Well you'll get no argument from me that the thermoelectric is very inefficient.
But the usefullness of this stove (the
Biolite - not the one in the OP) is not theoretical for me - I've actually used it and will continue to.
The USB charging is slow and weak - I have not measured the output but it typically takes several hours of boiling water/cooking with full bore flame to bring my iphone up from say 10% to 90% SOC or charge a pair of depleted aaa batteries (with usb charger).
But when camping it is not unusual - especially if boiling water to purify, cook and make hot beverages - to have the stove going for several hours. With a gas stove you would be worried about fuel consumption but with this stove the equation totally changes since a few minutes gathering twigs can provide an hours worth of fuel. (BTW - where I live in the Pacific NW of the US - gathering 1500g of twigs only takes about 15 minutes!)
Even without the USB charging I would use this stove because it's a very efficient rocket stove with the thermo-electric running a small fan that allows a very efficient, hot fire with minimal wood fuel. The usb charging - poor as it is - is just an added bonus.
Again - no argument that there are much better ways to charge an iphone, etc but in a situation where you're cooking anyways and the alternative would be carrying lots of batteries or using equally inefficient small thin film solar chargers - this bit of charging the stove provides serves a useful niche.