We have 7 cats in our house and this has worked out great.  While some of our cats don't use it, the ones that are climbers and those that have a need to look down on all their surroundings enjoy this very much.  There are many houses and levels making it easy for many of them to use at once.  

It was a breeze to put together.  The instructions were very easy to read and well written.  I would highly recommend this to people who have multiple cats.  I have found it to be very sturdy.  A few of my cats are large and I have not had a problem with it tipping or moving, even with a few of them playing on it.