My cat Cheddar has had a urinary blockage twice now. The first time it happened, we put him on Royal Canin SO to get rid of the crystals. He liked the food but he seemed to have an allergic reaction to it (developed sores around his ears and face). I switched him to Hills C/D canned after that. He liked the C/D, and it did the job of getting rid of the crystals, but I am less than impressed with the food overall. He started shedding a lot and seemed to lose some muscle mass as well. After about 9 months on the C/D, I decided to try and switch him back to a high quality canned diet (EVO and Wellness mainly, with a few other brands for variety). I gave both cats a little bit of dry food once in a while too. Well, a few months later (this past fall), he blocked again. Now he's back on the C/D.
I have mixed feelings about feeding him the C/D. I am not happy with the ingredients or the inflated price tag, and I don't like how it makes him shed a lot as a result, but on the other hand, it does seem to keep the crystals at bay, and that is what is most important to me. I am hoping that eventually I can find a food with better ingredients that does not cause problems, but right now, switching is not worth the risk. If he blocks again, I could very well lose him.
I also mix in water with his food to help dilute his urine- usually as much extra water as food if not more. I also went from feeding two meals a day to 3 slightly smaller meals since feeding smaller more frequent meals is supposed to help prevent pH spikes.
Purina also has a prescription diet for crystals, but I haven't tried that one. I'm also curious to know what other foods people have tried and what they think of them, especially for those that have cats with chronic urinary issues.