Yes, we just had a very scary experience with my 7 year-old cat. It started off as weekly vomiting- mostly hairballs, then turned into throwing up multiple times daily, and bloody stool. Otherwise he acted completely fine. After the multiple vomiting sessions in one day, we ran to the hospital, and they did ALL the tests. An ultrasound revealed that he had IBD and can ONLY eat crazy expensive prescription food. We have two cats (the other is overweight by a bit), so now they're both stuck on this health food. They don't like the dry food (that's much cheaper) so we were told that we could add a rabbit protein wet food on top. Well, since the new diet- which has only been about three weeks- there has been NO vomiting and no bad smells from the litter box. As a bonus, the other cat has already lost some added weight.
We can't even buy this food at Petsmart without his (the cat's) medical prescription. Aside from the price, it's been great. His coat looks better, he smells better, no more barf, no more bad bathroom smells, and he sleeps through the night in my arms instead of pacing- it also drastically cut down on his bouts of FHS. But really, the price of this food (and considering how little they eat of it-as they're grazers, and I don't want to leave it out for days... is something that will have to be figured out after the little guy recovers a bit. (We still give him anti-inflammatory meds on occasion.)
Some cats and dogs genuinely need this to live a normal healthy life. I don't know if the pet store sells the RX brands, but if they do- kudos to them, because these foods are hard to find. Although I suppose they'd need a vet (vet pharmacist?) on staff, as we needed a vet to review our prescription before we were allowed to buy the darn food!