Medsailor, glad to hear from someone who has had liveaboard experience with a composter. I don't live aboard, though I do cruise, sometimes with large crews, for short periods.
The material that comes out of the composting compartment is much, Much, MUCH less noxious than what used to live in my holding tanks. And the whole thing smells a great deal better than the hoses, pumps etc. that used to pollute my head. Plus I gained a hell of a lot of room getting rid of all that hardware.
I have not been in a knockdown with one of these heads but I can tell you that nothing is going to come out of the composting compartment if the boat spends any time beyond horizontal. It is firmly bolted down and with the trap door between the compartments closed nothing would make its way out. I can't make the same bold statement for the contents of the urine bottle, though if the boat spends much time beyond 90 degrees, a few ounces of urine loose in the head would be the least of my problems. Also, how many mostly full holding tanks are secured well enough to withstand that kind of treatment? I have seen some that would be on the overhead in a knockdown, with much worse consequences than what would happen on my boat.