We have been using ScoopFree Sensitive Crystal Litter Trays (3-Pack) for a little over 6 weeks now. I change the litter every 3 weeks. The crystals start to change color from the cats urine so it it easy to recognize when it needs to be changed, There is virtually no smell like I use to experience with a traditional litter box and litter. I am very satisfied and so is my cat.  A+ product.