Can I feed my cat Royal Canin 32 if it suffers from urinary crystals?

My cat has been having urinary trouble for about a year now and I have been feeding it wet food, but it seems he got tired of it and does'nt want to eat it anymore. So I went to a store today that sells hills and Royal Canin. I told the lady that works in the store the problem and what I am looking for and she said my cat would not develop crystals if it eats this food and also said people prefer Royal Canin to Hills so I got a huge bag of this food. So when i got home I saw the food is mainly for hairballs and maintaining a good weight for your cat. (She gave me Royal Canin 32 Fit). So basically I would just like to be assured that this woman was telling me the truth when she sold me this food.