Hi Colette,
I have the 28-inch "Studio Step" that you referred to. I recently upgraded to the full-size (43-inch) Original Step and it makes a huge difference. However, it is hard to find a good place to store it! For now, mine lives in the coat closet when not in use.
Anyway, to your question, I do not like the "Studio Step" at all. It feels wobbly and unstable, plus, since Cathe uses so much of the surface area of the step, you really have to be careful of falling off and hurting your ankles. I have also used the Reebok Step. I like the Reebok Step, but you can still notice the size difference between that and the Original Step. I was torn between the Reebok Step and the Original Step until my sister (she's a personal trainer) said, "just pay the extra 20 bucks and go for the gusto!" I'm glad I did. The other benefit of the Original Step is that it is easier to use as a bench for weight-lifting because of its size, and it goes higher than 10 inches--the maximum height of the Reebok Step.
Anyway, just my ideas! Take it or leave it!