I've had one for over 25 years - at a cabin in the woods, off the grid. It's way better than the outhouse it replaced. But it in no way lives up to the hype and never in a million years would I put one in a confined space like a boat, nor inside any living space such as a cabin. Note that I said I have one at a cabin, not in a cabin. Ours is in an "outbuilding", which is where it belongs.
It is supposed to decompose the waste with an aerobic reaction, thereby generating enough heat to evaporate urine and to maintain vent flow up a chimney and avoid unpleasant smells due to anaerobic byproducts. The fairly large one we have is supposed to be able to handle a family of 4, allowing you to periodically dump solids to the finishing drawer, where you can wait for breakdown to crumbly black mulch to happen. Well, no chance all of that will happen.
The ventilation and aerobic aspects work for the most part, in comparison to an outhouse. Most unpleasant smells are avoided but not all: it is still a giant bucket of crap with an opening on the top, and is nothing like a household toilet or a marine head with holding tank. It does not evaporate all of the urine and you have to do something with it. It does not keep up with a family of 4 (since that's what I have) and the solids build up if you are using it regularly. And then you have to get rid of them before they have fully degraded.
I've seen it said that it will work better on a boat since you only use it on weekends and the solids would have more time to break down. Maybe. But most boaters when out on a summer day have friends along and people are drinking beverages. 99% of the waste is liquid. So what are you doing really? Trading a 10 or 20 gallon holding tank that you can empty at a pumpout station for putting urine into gallon jugs (which is what the marine versions appear to do) which you may have to swap out hourly and put somewhere on a rocking boat so that nothing smashes into them and makes them spill? And then what solids there are, you are leaving cooped up in your boat cabin all week for you to come back to?
It makes no sense. Really in that setting it is inferior to a Porta-Potti.
I recently saw an episode of Maine Cabin Masters where they put the very model of this which I own into a bathroom in a cabin. I just thought "idiots, they'll be sorry". They redo a cabin and make a nice space for the family's kids to sleep, and it's going to smell like a gas station bathroom much of the time. It's a head scratcher as to what people are thinking.
