You don't usually dump the composted poop into a landfill. That would be a last resort. It is fertilizer. It goes on plants.
Since you have one I defer to your experience but I'm not sure it is accurate to call what comes out of the composting head, compost ready for plants.
It takes time for composting to happen and depending on your usage some of your deposits may or may not have composted. If for example I have guests and the bucket is full I have to empty it now and can't wait for a few weeks for the last deposit to compost.
I believe what some people do is have a spare bucket or two that they can stash somewhere for a while till it really becomes compost.
This brings up what for some is the most significant issue.
If you have a plot of land where it is easy to dispose of your home-made compost and your usage of the boat is such that you don't generate that much and you have a place to "cure" a bucket or two of fresh stuff and you don't have that many people using it and they don't have any medical conditions that would create and excess of of "intermediate" deposit then the composting heads will work great.
Many of us however have no back yard as we are cruising or live in an apartment or condo.
It is highly unlikely that a marina or landlord will be happy with our home made manure. It has to be aged appropriately and how will they know that was done.
The other more minor issue is that the pee bottle has to be emptied very regularly, probably daily. Depending on your location walking it the the on-shore restroom or dumping it overboard and not letting your neighbors see you may get tiring.
The purpose of this post is not to put down the composting toilets, their are obviously some people that find them perfect for their use.
They never have to deal with hoses, pumpout stations, broken, valves, lime buildup, joker valves, through-hulls and a host of other problems.
They do however have to deal with one or more buckets of "something" every few days, or weeks depending on usage, the pee bottle daily, fetching and storing the moss. Many folks find they have to treat the bottle and the bucket with something to make it all work properly.
So both systems have their advantages and disadvantages and different folks will make different choices.