Has anyone tried any immune products on their cat?

[BellaBooBoo]

My cat has severe allergies and we have done everything to try to help her. We have switched her food numerous times. We can't seem to figure out what is causing it. We know it all started with a flea allergy, but the fleas have been gone for over a year and she still has allergies. I ordered a product called Only Natural Pet Immune Balance because it had really good reviews. I'm waiting for it to arrive and hoping it helps. I'm just wondering if anyone has tried this, or any other immune booster for cats?