I don't have any experience, but I do want to add that there are certain times these diets can help-- but usually only for short term and can sometimes come with a price, as in allergy reactions to the food, as long as you are aware of these then it does make it easier to try it out, knowing what the possiblities may be.
I also want to point out that a vet will likely recommend these foods to anyone who brings their pet in for a UTI-- regardless of severity. So when, my question, is it TRULEY needed? There certainly are times, but know when is the hard part.
@agingermom just went through UTI and stones so maybe she can give you more insight.