Well all 'complete' cat food hold the correct vitamins and nutrients that a cat needs, whiskers included, but many cat food brands pack their cat food out with fillers such as maize.
Whiskers is by far not the worst food out there, but it does only have a 4% meat content, considering cats are carnivors, this does seem a little odd. Most people (myself included until I joined this site) do not read the back of cat food packets, and we just go by popularity.
Your not doing anything wrong by feeding whiskers, but it is worth bearing in mind there are some cat food companies out there with up to 90% meat in their products. This is a big difference.
Also alot of people who look into the meat content in cat food find brands like hi-life and natures menu, these will cost you considerably more than you are paying for the whiskers. I used to feed felix and wanted to change but found the price of these food too high (especially with 4 mouths to feed).
I did some investigating and found Bozita cat food (from
Pet Supplies, Pet Food, and Pet Products on Sale Now at zooplus.com) this is actually cheaper than whiskers (and felix) but has about 88% meat.
The only thing with Bozita, is it is more of a jelly consistency, so if your cat is into gravy, then it might not go down too well. Although I must say, my very fussy eaters loved it.
Anyway, just a bit of food for thought. Btw, there are some people on here that really know alot about feeding cats, I have lernt so much since joining this site.