What's the difference between a stair stepper and a stepmill stair climber?

A mini stepper (like the sub-$100 folding models here) uses two hydraulic or magnetic pedals that pivot in place, while a stepmill or 'continuous climber' uses a rotating staircase that you actually climb, the format you see in commercial gyms. Stepmills offer a more authentic, higher-intensity climb but cost far more and take up significant floor space.