Cassette toilet vs porta potty

My pre-Tiger, which I camped in often and happily for 15 years, had a PortaPotti which was inside an enclosed bathroom area which also had a sink with running water and a shower. It had no black tank, just the PP's own tank. When I wanted to shower, I could lift the PP out onto a rubber mat in the living area and then have a shower stall big enough to use comfortably. Cleanup after the shower was easier than drying off a whole wet bath area. Emptying the PP was not a problem either on the road (into dump station or camp toilet) or at home (into house toilet). The PP tank does not have the wheels and handle often found on cassette toilets, so you have to carry it. A PP seals well and creates less odor than an RV toilet plus black tank; do watch out for altitude changes. If something breaks on a PP, you can buy the parts to replace it; I had to do this several times for the pump bellows. For extreme boondocking, you could use non-potable water in the flush tank; I guess you could also do that for a cassette toilet.

If you need extra tank capacity, you could buy a second tank and switch them out; you could also do that with a cassette toilet. Either way, you would have to have space to store the second tank.