Clay comes in 3 grades - regular for heavy duty use (badly contaminated paintwork), medium and light. It removes all contamination on the paint. Try Bilt and Hammer MAF - you will realise there's no substitute for it. I'm not saying there isn't some benefit to Iron-X, but this wouldn't remove all debris from the paint alone just by spraying it onto the paint and rinsing. You feel and see the clay picking up crud as you take it over the paintwork. I definitely wouldn't machine polish without claying, you will just be polishing the crud into the paint causing more swirls than you started with.
I think Iron-X will be a useful addition though to use mid point between full details when I don't want to clay, every few months or so. I'll try it and report back.
Cheers, Simon