I bought this and another brand for rescue cats in a custom built "cat shack".  Unlike the other brand, this one is quite stable and doesn't even need a corner to keep it from falling over.  It's against a wall near a window and has kept wobble-free for about two years.  It withstands 2 or 3 cats at a time.  The boxes are large enough for a cat to park and nap.  I even had two who shared one of the boxes until they got familiar with the caretakers and surroundings.  The covering could be denser, but it seems to be holding up fairly well and sandburs and debris can be removed fairly easily.