So I've seen a few ads for these small devices you hold in your lips and breathe through, with adjustable resistance. You know, names like "The Breather" and "Expand-A-Lung." Look kind of like whistles. They claim that over time this strengthens the muscles used in breathing, increases lung capacity, etc etc. They sell for about $25. Has any one every tried one of these, or know if they might provide any benefit? It might be good to play around with while I'm driving to and from the office.