I think 50% extraction is probably a bit optimistic as the peak efficiency is 59% for all turbines. 7m/s doesn’t seem too high for a summit though 
Reading between the lines I’m guessing they have batteries included so you can store up energy gathered over time with varying wind speeds and use them to power/charge something else.
I had a look to see what was available in the folding solar arena and there are lots of things available really quite cheaply. Such as 28W folding arrays for $100US. De-rating by 50% gives 14W capability for only 1KG in weight. What would be useful is a solar array you could deploy on the rucksack so you could gain some charge whilst walking.