I have used one for a long time... and most anyone who has borrowed my gear for a dive - has purchased one right away... Because they really do make a pretty big difference.
The air coming out of a tank is .1% humidity. With each breath, your lungs have to moisturize that to 100%. Even if you find some way to stop your mouth from being dry by some method... you are still not fixing the problem of breathing dry air - just eliminating one symptom - dry mouth.
The #1 contributing factor to DCS is dehydration, and the #1 reason for diver dehydration is breathing extremely dry air.
The Bio Filter will increase humidity to about 50%, tapering off to about 30% near the end of the dive if a very long dive.
The new ones can be refilled without opening them up - a special one way valve and water bottle lets you just re-wet the sponge withoug even removing it. Yes you do have to remember to re-wet it... but forget once - and you'll make sure you remember from that point on - breathing the moist air will spoil you! And it's easy and fast - so yes you must remember all those little things like wet sponge, turn on air, etc. Not much of a problem for me... and I don't even use a written checklist!
Actually Joe, (from the ask Joe & Larry) got heart burn so bad during every dive - he was going to give up teaching for the shop a few years ago. Then one day, he borrowed my reg, since he was rebuilding his, and the heartburn went away. Turned out the dry throat was letting acid effect him - but humidifying the air - the symptoms vanished.
So I'd tell you - they're great... Won't dive without it. We've sold hundreds of them.. and have not had one single problem ever with them other than someone who stored it with the sponge in and crancked together very tight and it was a pain to open it up several years later.... but we did get it apart - cleaned up - dropped in a new sponge and away they went.
