We have a Wall Mart purchased port-a-potty that is simply a bucket in a container with a plastic toilet seat on top. We use it when we don't have water in the tanks (mostly in the winter for winter camping when we camp witout water in the tanks). Works perfectly fine, easy to clean out, and has lasted for years and years .. (well, the first one did.) We purchased our first one in 1999 and used it with our pop-up. Last year 2015, the metal handle on the bucket finally rusted into nothing. We purchased a new one from Wall Mart again. Hope it last for 16 years too!
I think Cassette toilets are a bit more complicated, and more parts to clean. Often they require using bags to catch everything. But the clean up is more involved.
Go for simplicity and spend your time camping and not clean parts from a toilet.