I have a sinus problem as well, though I have my doubts if any of these humidifiers or air purifiers work.

Nevertheless, I'm pretty sure they are not harmful. So I have a model that is an activated carbon filter. Generally, I hear that HEPA filter ones are the most effective ones though.

In any case, make sure to look at the prices of filter changes before deicing on any. That is pretty much the main hidden cost.