It seems to me that if you have time to pull out your hopper, and put in a new one, then you certainly have time to pop the lid on you hopper and dump in a pod, especially if you need to screw it in. And I agree, fubar, if theres not a harness designed for it, then carrying around those little things will be troublesome, and nearly impossible to avoid "ball droppage." It seems to be no less efficient to carry around extra 200 rd hoppers for when you need to load, and if that was more efficient, ballers would have been doing that for years.
Although, they are cool little trinkets, and for those who like piles of useless toys, they are perfect.