After getting Olly & Max litter crystals, I can't actually buy anything else for my kitty. If I ever struggle to get some of these, and have to (unwillingly) get another brand, within two or three days I can smell the difference. These litter crystals hold in any unpleasant odors the way that they should. All cat litters say "Can last up to a month", but I find that this is the only brand that really does, without everyone knowing about it because of the smell! Simply the best that I've ever gotten (this coming from a cat mom of more than a decade).