They're good for people with some disabilities.Recumbent trikes with 20" wheels sometimes appear around here. They have a rod with small red flag on top so that drivers can see them more easily.
There are many ordinary adult trikes around here, and electric power has made these much more handy. The only problem with adult trikes is that they have a tipping point which is usually only discovered by tipping over on a bend, and this is why I would not recommend them to anybody.
But they have the advantage of being even nerdier than 2-wheeled recumbents.