I did the same as Dan:
I installed a Thetford Curve in ours and it works well for us.
We only pea in it. We can go 5 days normally. It is cheap, lightweight, easy and clean. Whats not to like?
I looked at (and could always still change) the natures head. But most of the places we camp at have facilities and the cost of the composter was 8 times more than the Curve.
I like the way it looks and works so far. Can always go back to a black tank system if I want, or composter. Everyone's needs are different so just go with works for you!
As previous post indicated, spend the extra ten bucks and get a hold down bracket. It doesn't come with the bracket, and you don't want it falling over in transit!