Among other things. I really hate how a man's, well dangling parts for lack of a better PC term, hang on the "ramp" of the seat, which is always cold for some reason, and right where a gal dribbles. I could go on about things I dislike about the design, but some folks put up with it due to the cost of some other systems. As EM is so fond of saying, "Buy once, Cry once".
The Partner Steel offering is called the Johnny Partner and is constructed out of .125 aluminum. IMHO it's simply the finest most durable system available, and one MAJOR bonus is you can have your favorite sewn goods company make you a fly bonnet, basically a cover large enough to go over the seat, sorta like a womans shower cap, that will keep the flies out of the groover when not in use. Huge bonus is keeping flies out of the groover, as they may eventually end up on the food in the kitchen. It's a true pleasure to sit on as well, VERY stable compared to a rocket box system and almost impossible to soil, making groover duty so much easier and dare I say, pleasant. Not to mention it's relatively light when empty and holds a tad more droppings than the other offerings.
Jon-ny Partner Toilet is the link. Not cheap, but a lifetime purchase..
The Selway is an inprovement on the old "River Bank" toilet, which used to use a 5 gallon bucket inside with a improved latching system for the lid. Now it seems they are rotomolding the inside container which they are calling a vault, way spendier than the initial 5 gallon bucket. Still a good system, better than the rocket box systems out there, and again, a LOT lighter