These stairs are sturdy. To all those thinking about buying this, and are concerned about the negative feedback about the stairs being flimsy. Don't be. These stairs have been improved; they no longer come with a strap for securing. It appears that they've been redesigned, according to the booklet that came with mine. 79400 Series Updated February 2018.

These redesigned stairs have a board (See #2 piece in diagram) that stabilizes the the three back steps to the base. The shortest step in the front, is small enough to be sturdy on its own. 

Five stars from me. And the cats love it; they immediately started using it the day it was assembled.