Faced with a problem in my after head last year (I don't know why J boats decided to put two heads in a 40 footer, but they did) I decided to take a chance on a composting head. I figured I'd keep one head with the usual holding tanks setup and try a composter for the other, thus having a backup if either failed. When I cruised to Nova Scotia last summer the one that failed was the standard head. A guest of the PO had dropped a sanitary product into the thing and jammed it up - a fact I didn't discover till I took the system apart.
The jammed head made the whole forward part of the boat practically unusable. Of course, we didn't know the system was jammed and at one point I looked at the holding tank and saw it was bulging in all directions, really ready to burst. I had visions of the thing exploding and me running the boat ashore, leaving it there, never to return. So, while offshore, I had to open the deck fitting, resulting in a two foot high gyser of you know what. It was at that moment that I decided I would never have a holding tank system on the boat ever again as long as I lived.
Meanwhile the after head was happily doing its job, without odor or problems. I realized that if there ever was a problem I would be able to take care of it offshore by removing the bottom part that holds the "end " product, tie a line to it and dip it over the side a few times, till clean. Much easier way to deal with a problem than the myriad hoses, valves, tanks etc of the standard system.
I am a total convert to the composting head solution and last year removed all signs of the holding tank era, using clorox to try to remove the lingering odors. This spring I took the compost (and it was compost by spring) out of the after head and dumped it in the woods - I'm still too chicken (and afraid of the wife) to put it in the flower garden.
Last week I sealed the sea cocks for both heads, installed the second Air Head, and the space previously taken by two holding tanks, assorted hoses, valves, pumps, etc has been put to much better use (the forward 20 gallon holding tank that nearly burst has been replaced by an auxiliary 20 gallon diesel tank that increases my fuel capacity by 40%)
I never experienced any odor problem. I did not use the supplied 12 volt fan, not wanting the constant drain on the batteries. Instead I use solar vents that keep the air moving without taxing the electrical system. Although I only used the composter for the second half of last summer, I never had odor problems of the kind I saw (smelled?) on my boats in the past. Incidentally, I have no connection, financial or otherwise, to any composting head maker. I just love the product, at least compared with what else out there for the purpose.
More than half a century ago Dick Nye, owner of the legendary Carina asked Olin Stevens advice on what to bring on a Transatlantic race. Olin said " a stout oak board with an 8" hole and a 100 pound bag of coal". Dick wondered about that but decided to follow the advice anyway. Sure enough it was cold as all getout on the race and all 100 pounds of coal went into the stove. The stout oak board? It had to be jury rigged to the pushpit when the head died hafway across. Wise words from a wise man.