I have two cats using this, one is 7 lbs the other 13 lbs and they both love this! The 7 pound sleeps in the nest while the older cat spreads out on top perch. 

Pros: Perfect height for cats to look out the window and bask in the sunshine. Very easy to assemble & the hanging rope is a favorite for both cats.
Cons: Base and top perch are same size, causing unit to rock a little when both are climbing at the same time but it is not bad enough to tip over.