Re: Air Head Composting Toilet or Similar Mfg.
Based only on what I've read, I think I'd be inclined to go with a composting unit if I were faced with installing a head system from scratch. It would be much cheaper and easier to install since it avoids much of the plumbing hassle. In my experience holding tank systems are far from odor free as well, so I somewhat see it as a "pays yo' money and takes yo' chances" proposition. There are unplesantries with either system. Pumping out is not exactly a fun hobby, but neither is carrying out bottles of piss and bags of crap.
If you weren't happy with a composting system, it would also be less hassle to uninstall and replace with a traditional holding tank system than the other way 'round.
s/v Palmetto Moon
1991 Catalina 36