N95 masks used during SARS (a virus) and effective, unless – say – someone push up the mask to scratch itchy nose.
I tried one, once, during the outbreak: horribly unconfortable; hot n humid air, even worse than normal hot n humid air in HK. Tried the nigh-on useless (unless you happen to have a disease yourself and don’t want to pass it on) paper masks. Otherwise, with SARS mainly in hospitals, went mask free.
Can’t imagine more than tiny number of people in areas actually affected by H5N1 virus (rather than by bird flu fearmongering) will use masks; and those that do perhaps in factory farms, where masks etc should be supplied by companies, or veterinary support etc, also supplied with masks.
Otherwise, these masks surely beyond reach of people in areas really affected by bird flu; and unlikely to be worn anyway.
While if aiming for sales to the paranoid: well, shame on viraldefender.com.
See also this summarised paper on CDC site, about making masks from t-shirts; not ideal, but judged effective: