just got back from dumping the buckets we’ve been living with one for over 2 years in a rural setting … and we were really scared of this change when it first arrived in our lives (we didn’t have any choice).
there are generally two directions to go with humanure/composting toilets: (1) ready made industrial solutions - of which there are many; (2) do it yourself composting toilets with sawdust (or alternate covering material).
it is true that option 2 is fairly easy and very cheap to build (and its way cool that the toilet isn’t anchored to the ground) … but that’s only part of the picture. another and more challenging part is where to put the humanure. If there is an outside space for it then a “humanure hacienda” can be built … this may be tricky in an urban setting (even if you have the space for it) in terms of local building codes/regulations.
you also need a regular supply of two things to operate a humanure toilet of the DIY kind: (1) organic matter like sawdust to cover humanure in the toilet buckets; (2) organic matter such as hay to cover the dumped humanure. you need to check on the availability of these things in the area (again, this is very different in a city setting then a rural setting).
If used correctly (though it isn’t very complicated people who are not familiar may need instructions and a certain amount of discipline) … there are no smells neither indoors or outdoors. I believe a composting toilet is more hygenic than a regular flushing toilet.
in terms of capacity the DIY option is unlimited. there should be spare buckets (4 per toilet) … but capacity is only limited by frequency of carrying out and clearing the buckets. other industrials solutions come in different configurations for different capacities.
It can be a huge savings in terms of construction/installation/plumbing. The same is true if during renovation you can get grey-water to flow by gravity from sinks and showers directly to garden areas … makes all the plumbing simple and cheaper (but again check regulations - or live outside the law consciously).