We fitted a natures head last June. We are full time live-aboards in Cowes UK.
With just the two of us onboard the head lasts about 30 days.
There is a slight smell, like damp earth or soil, not in the least offensive.
The head is cleaner and nicer to use (we do not use the coffee filter option) Men
can use the head to pee into when stoodup as long as the flap is closed. We find that the head needs the toilet paper it helps to absorb the excess moisture but can make turning the handle difficult if it is is long lengths (3 sheets
seems to be ideal).
We empty the urine jar every night no matter what the weather
(one overflow is enough), the urine smells bad, a tea spoon of sugar helps to mollify this smell. The urine is emptied in to the sea, it is not a pollutant, even the US CG agree with this and have OK'd the head for use in the USA.
Friends and visitors often need to be assured that this is a normal thing to do (the guys often want to pee into the peat (named Pete by us for ease of description, the urine jar is known as Mike, named for a friend who takes the piss all the time)) area even after a careful explanation of the workings. The lack of a flush also seems to confuse some folk.
We have had a little illness, the runs just required a little extra peat, if you are going to vomit use a bucket not the head.
Over all we are very happy with the Natures Head, we would like a second Pete bucket and a second Mike jar just for ease of use and being able to leave the solids to compost for a second 30 days, these are not available in the UK just yet.
Hope that this helps?