"A composting head is so superior"
Glad you like your glorified cedar bucket, but there are in fact no composting heads for boats.
What you have is a bucket that collects fecal matter, which is still "live" and still has to be disposed of someplace, sometime, and it ain't compost when you have to move it.
That the industry can't be honest about what it is and what it does--and doesn't do--speaks volumes as to why they haven't taken over the market.
No, sorry, not true. Composting begins right away in the toilet. It begins to break down and dry out almost immediately, because of the fan and vent. Yes, the composting process will not be complete when you empty it - just partially complete. If you can wait a few days after the last solid use before emptying, there will be no odor.
As the toilet instructions (and the websites) clearly explain, contents must finish composting elsewhere. A plastic bucket with holes punched in the lid works great. Then, after 3 months, you have a completely safe, environmentally friendly fertilizer. Compare that to sewage, which must be expensively treated, through a high energy process. This has a big ecological impact. Most sewage treatment facilities produce a highly toxic sludge which is then destroyed by yet another high energy process that is bad for the environment.
If you do not live aboard in the winter, you can leave the toilet for the season. In the spring, you will have finished compost right in the toilet. Two people using the toilet for a summer cruise and weekends will probably not need to empty it all season. Now, that is pretty incredible, isn't it? Not much like a bucket, you have to admit.
The best thing to do is talk to people. In my experience, everyone who has installed a compost toilet in their boat is pretty enthusiastic about them.
The reason why they have not taken over the market is the retailers cannot get them to sell. They are sold direct by the two manufacturers. The marine store guy is not going to tell you that a drastically better and much lower cost system exists, will he?