A composting head is so superior, in so many ways, that it's almost ridiculous. The reason why people still buy complex, insanely expensive, space consuming and smelly holding tank systems is that the two models of marine composting head are not sold through any big marine retailers. Stores would poo-poo the idea (pun intended) because there are no dollars in it for them. The sales guy will sell you the holding tank system instead.
Think about the advantages of composting heads - no odor. Ever. Holding tanks and hoses stink. Get rid of at least one thru hull. Gain enormous storage when you pull out the holding tank. Save considerable dollars. Forget toilet maintenance, these things are almost maintenance free. No rebuilding, no leaks, no plugged hoses (yuck!)..., Forget searching for pumpout stations or spending your precious time pumping out. Get used to having to worry about emptying only about once a season for part time boaters, every six weeks for two people on a cruise. And finally, produce compost instead of toxic sewage which must be treated, then the highly toxic sludge must be transported then disposed of using a great deal of energy. The carbon footprint is huge. Holding tanks are very eco-unfriendly.
Now, what were the advantages of holding tank systems again? Oh yeah, none!
I've got a Nature's Head and my neighbor has the Airhead. Both are good. This dealer for the Nature's Head
was very good. There are others.