Does your cat have chronic renal failure?
What else are you currently doing for him (diet, medications, etc.)?
I do know some about the oil, but haven't personally used it. It certainly isn't going to hurt your cat, and so I would go ahead and try it.
Its also important for cats with renal failure to get plenty of fluids, and for this reason if you feed a dry cat food I would recommend switching to or at least supplementing with canned. Its also important to use a food with a high quality protein source and low levels of phosphorus. Here is a page that tells this information on many different canned cat foods:
If your cat doesn't improve soon you might want to consult your vet about routinely administering fluids, and a prescription supplement called Azodyl. We have had good results with this at the clinic I work at. Here is a page about it:
If you have further questions let me know. If this answer is helpful please click accept. Thank you and best wishes.