3rd, the Apollo Bio Filter - even if you don't have the phlegm problem, this thing rocks to help dry mouth
Dan,
How deep have you had the Bio Filter? Have you noticed any change in your breathing resistance, especially with exercise? I didn't see any information on the company's website about the effect (if any) of the product on actual or perceived breathing resistance so I'd be interested to hear your perspective, along with that of anyone else with experience with this item. I'd also be interested in hearing from the manufacturer about any testing that was done.
Thanks,
DDM