Product review (4 stars): Refilled cartridges tend to clog, at least initially
I have two Air-o-Swiss humidifiers that require a couple of filter changes per winter. The cartridges are very expensive, and so I've used the packet refills (with ionic silver) instead of buying new cartridges all the time. However, the packet crystals can clog the unit, causing it to act as though there's no water in the tank.  It can take up to two weeks for the crystals to 'settle', allowing a refilled cartridge to work properly. In the interim, you occasionally have to shake the tank vigorously to get water to flow again through the cartridge.  I bought a spare cartridge in case the clogging becomes intractable and I grow tired of shaking the tank in the middle of the night. So far, this hasn't happened -- the refilled cartridges are working just fine. I've read that the clogging problem can also be resolved by using less than the full contents of a refill packet, but I haven't tested this solution myself.