There is very little differences in the cassette and modern porta potti's like the Tretford Curve.Myself,boondocking 100% in the mountains of Idaho I would/do prefer the Cassette/Porta potti over the black tank, that I have to go to town to dump...
It takes quite a while to fill up a 5.5 gallon porta potti when most all of Number 1's are done outside and a forest service outhouse is usually way closer than any town with a dump station.
I have even thought of pulling out my TC toilet and replacing it with a PP..