Exactly! What we are discussing here is an ad-hoc solution. That $4 device will work for how long? A week? A month? Then we're up for the next one. A continuous stream of aid is necessary to keep this solution going. So, it's not sustainable, assuming we don't consider permanent aid a sustainable solution. (I don't.)

I agree, it is not a primary solution. However, in a world increasingly plagued by natural disasters, well water can often become unusable, and in those disaster scenarios devices like these can save lives.