You have a long many times contributed to thread on here about composting heads. You might want to read it. I have been living aboard
for 6 months and for 2 months I used nothing but the on board natures head just to test it out. No smell, no chemical treatment, no problems. No holding tank
, no hoses, no siginificant moving parts, only a crank on the outside and an agitator on the inside.
With the trend for no discharge zones seems the composter is the best of all worlds.
Downside= will not support more than 2 people for an extended period of time, however if at sea then emptying on a calm day is no problem, when in port, whatever system is chosen it is best to use shorside facilities asap, of course.