i dont understand how the concentration would have some special effect in and of itself, but i could see that nothing above a certain concentration would keep the particles at a minimum size for effecting viruses and working inside of cells. maybe thats what they are talking about. i have heard many times that the lower ppm is much more effective internally.
externally, i think the higher ppms is fine, maybe even an advantage. but then, it still depends on what the problem is.
bottom line is, if every houshold had a cs maker, it could easily cut doctor visits in half nationwide. that would be an economic disaster(tsk, tsk)