Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Best one if you know secret

I understand the poor reviews because of a tipping over problem. However, this one works best for my cat because it is wider at the bottom. I solved the tipping over problem by placing a 4.4 lb plastic weight that goes on a barbell inside of the bottom opening. My cat weighs 15 lbs and it works great. I'm sure not everyone will have a set of weights to use but could substitute something else.