One of the first things I noticed is the Navage is cleverly designed to force you to use up those cartridges. I am fighting really bad allergies right now and I need to run two or three fills of water before I can breathe through both nostrils.
The instructions say the cartridge system is designed so you cannot feel the shock or discomfort or whatever of running straight water. And it seems like they've done a good job of stopping you.
Except you CAN run straight water. Here's the hack. Leave your last used cartridge in there. Then run warm water over the back of the lid, over the lid hinges. The water will seep into the tank. You can run a cycle or two on straight water, then a final cycle with a cartridge. With my passages clear, I immediately inhale a nasal spray type anti-allergy treatment.
Bottom Line: Yes, I would recommend this to a friend