I have seen them as well, but haven't bought any. I'm sorry I can't answer your question! If no one else on here knows the answer, you could always ask your vet
My vet gave me vitamins for my Louie when he got neutered. They did bloodwork and found that he was a little anemic. But I think if a cat or kitten is healthy and getting all their needed nutrients, vitamins are not truely needed.
I don't think vitamins are necessary if you are feeding a good quality food and you keep your cat up to date on visits to the vet and everything. Do the basics and the cat should be fine. Now if any problems or diseases come up then you might want to talk to your vet about vitamin suppliments. Lysine is a good suppliment that my shelter uses.
I only give vitamins to my formerly emaciated girl, Lola...she needs them. Leo only gets Lysine because he tends to be susceptible to colds without it.
I may go get some vitamin stuff again--Lucifer had a horrible case of fleas back up in NY because of someone continually letting him outside despite my wishes, and I had to give him this spray stuff on his food because he was just so lethargic and sickly. The flea meds I got from the vet helped, and we got rid of them from the house, but I think without the spray he would have taken a much longer time to recover.
After the fleas ended, on the rare times when he was looking a little off-kilter, or had paler gums and whatnot than usual, I'd add a spray or two to his food for that day and he would be shipshape again.
Best just to be prepared, I suppose.
I just give Lysine to my cat. But I think some cats need vitamins if they are not on a balanced diet or a vet prescribes them, otherwise I don't think they are necessary. Most of them are for things like Shedding or a glossy coat. Just a way for pet companies and manufacturers to make extra money.