We've got 3 of the little darlings. 2 x 18 year olds and a 2 year old. So, here is what we have:
2 year old loves mice and rats but will not eat tinned cat food of any sorts
1 x 18 year old has thyroid and heart problems and is borderline kidney failure
Other 18 year old has a very delicate stomach and can only eat Felix senior
2 year old won't eat tinned cat food but will eat the other cats food, including the renal diet food, and any dried up bits that fall on the floor before we clear them up
1 x 18 year old will eat any type of food apart from her renal food but shouldn't
Other 18 year old will eat absolutely anything, including thai curry sauce, and particularly things that will make her throw up
So now the 2 year old gets fed in a different room, one of the girls has her Felix on the windowsill and we let the other one (renal case) eat what food she wants.
Interestingly, the one with the renal problems had a blood test a few weeks ago and her creatinine and other renal tests were slightly higher than normal after eating normal food.
I am very suspicious of these specialised foods to be honest.