I bought 2 sets of these, and put them back to back for play for a very active beagle I have.  She loves them--runs up and down for treats, and even sits on them just because!  She's only 20 lbs. but they're on heavy carpet, and they don't rock or tip--the center of gravity on these is just right.  So glad I found them!

Pros: Great price, easy to set up, sturdy and lightweight.
Cons: none