Have you tried LID diets and novel proteins first? Sometimes it can be as simple as trying that and less expensive lol. Or a raw diet can help some cats with bad allergies to.
Since you aren't getting any responses in this Forum, you might try over in the Health Forum. I'm guessing the suggestion to try one of these foods is the result of possible allergies or other health issues that aren't being resolved otherwise correct? So it wouldn't be untoward to post over there.