There are many prescription diets that are appropriate for urinary crystals besides just the SO. Talk with your vet about other options FIRST, BEFORE changing diets.

You could take Karen's suggestion and compare ingredients to other OTC diets, but make sure to talk it over with your vet first, understanding that while some OTC brands may claim to be for "urinary" issues, none of the OTC foods have gone through clinical trials to be able to make legitimate claims like that. The prescription foods have.