On almost all of them you also have to run a vent tube out the roof and have a low amp electric mini-fan that runs all the time. Otherwise the decomposing waste....well......you know.
I think it takes about 4 weeks for the waste to completely decompose. On a short trip, you can come back, let it sit and decompose, then empty it. I believe that on a long trip, it fills up and you have to empty it with the latest ...um...deposits still....um...new. Then you put in more peat moss.
Also, I think you have to turn the mixing handle to mix moss and waste at the end of each use.
Still saves use of fresh water and place where black tank goes could be used for something else. Urine is sterile unless you have a bladder infection, so it can actually be dumped in many places.
If you put this on a SMB with penthouse roof, I would think the vent pipe needs to telescope and may not be air tight. Maybe you can vent it through a 90 degree elbow out the side. IDK, but I've never seen that and people passing by the side of the van....not such a pleasant smell for them.