I think if your cats are doing well on Innova, keep them on Innova. I have heard that Wysong is good for some cats, but not for all. Some cats find the food too rich.
But if your that curious, just try it out and see how your cat's respond. I think the Wysong wet foods require extra supplements so make sure you read what is required on the label.
I've been researching commercial cat foods, and both Innova and Wysong seem to be very good: high in real meat and low in grain fillers. Wysong sells a line of canned food which is basically just meat, without any other nutrients - you would treat this as a raw meat diet, and add supplements such as bone meal, etc.
Some cats may do better on Wysong vs. Innova, or vice versa, but both brands are much better than the mass-marketed grocery store brands (where the "meat" may actually be rendered from euthanized pets). Look at the ingredients lists and you'll see how similiar Wysong and Innova are.
Well, I'd personally try to figure out why they want to switch you. Does the vet sell Wysong? Are they getting any incentives for getting you to switch? Just some things to think about
Are your cats generally healthy? If there are no special dietary requirements, I would stick to the Innova simply because they're used to it. If you do decide to switch over, you have to do it gradually so as not to upset their stomachs too much and not cause them a lot of stress. Some cats can switch over foods overnight but many others need some time to adjust.
Thanks for the link, Tasha.
Sorry, I don't have any experience with Wysong, but I really like the Innova food, even though I sometimes have difficulty getting it here, since it is often held up at customs, and German suppliers frequently run out. Supply problems due to inclement weather, for instance, are one reason why it might not be a bad idea for you to alternate Innova and Wysong, provided they like the latter and it agrees with them. Another reason is that it is very difficult to get cats to eat prescription diets once they've gotten used to only eating "their" particular brand. If they're accustomed to some variety, they're more likely to agree to eat something new.