Work very well for our Yorkie Sisters at nighttime or when we are away from our home.  Lots of freedom for them to move around and stretch inside.  We have even double decked them, one on top of the other like bunk beds, and they are very secure and will not topple over preventing any kind of an accident or injury.  For anyone who might try this setup, just make sure, do a test first, that they Do Not Move or Wiggle.