Hi Alterna,
I'm not entirely sure since coudn't find anything about this difference online. But having just bought a RX533 I noticed the chassis is made completely from plasic. This is different than the aluminum of which the zenbook has been appraised for, so I think only the UX model comes in aluminum. Also i noticed that the screen slightly moves when I type, not to disturbing but might be better for the full aluminium one.