Instruct: Classify Amazon reviews into positive or negative sentiment
Query: expensive but worth it with liners

I buy the six pack and it will last a year thanks to the liners I found that fit inside the tray. 1 tray lasts me about 2-3 months with the liner inserts and store bought crystals. (Bare in mind I have 3 cats and 2litter boxes so I am replacing the liners about once a week)