I could only find a few accounts of boaters using these.
Here's two that were somewhat detailed:
http://www.woodenboatvb.com/vbulleti....php?p=1569460
http://www.sailsarana.com/FAQ.htm#why
All swore by them, and one was newly installed, and he was ok
so far, but he didn't follow up.
They note the only drawback is the small size of the urine container.
I suspect they all just dump the urine over the side - one admitted it
- but in any case a container of **** is easier to dump into a shore
toilet than a load of crap.
It's hard to say for sure, but it appeared most of the owners were
cruising couples, or couples with small children. There were notes
about guests aboard, but no mention of parties. I'm assuming the
holding tank/pumpout method is best for those who get heavy traffic in
the head, but may even be wrong about that.
According to these accounts they have no holding tank, no plumbing
issues, no thru-hulls, no stink issues, and gain considerable space.
The only power used is by a 12V fan (50-120mA, depending on which
account) which is supposed to run constantly. One uses a solar
powered vent instead of 12V and says it does the job.
The footprint is small, same as a porta-potti, but the Airhead is
taller.
I suppose there aren't many accounts because it is a relatively new
system (2002?), and they are expensive - @1k.
Not bad when compared to the cost of a new holding tank system,
but most cruisers already have a holding tank system, so the incentive
to spend the 1k to replace instead of smaller sums to keep on fixing
it is negative.
The urine/solid separation technique appears to be gaining favor
in some areas of the world, and makes sense for a few reasons,
biological and mechanical.
I'm planning to buy some kind of cruising boat, and if I can avoid
playing sewer worker as part of the "cruise experience" - good.
I've read too many stories about **** disasters to wish it upon
myself. Spent some time doing sewer tile work in 6' trenches, and
had all I need of playing Ed Norton, even at a pumpout.
Another thing that turns me from the current holding tank method of
waste is just driving over a bridge where there's a crowded marina
below. Smells like crap. Maybe that's just my limited experience
near St Pete Beach, and maybe that's home runoff into Boca Ciega Bay,
but I've read a lot of cruiser stories about filthy harbors.
And bilges.
I'm really interested in hearing a thorough review from anybody who
uses the Airhead, or even second-hand info from those who know people
who have them.
But any comments are welcome. I'm a boat head newbie.

--Vic