Pros: So similar to human-style food!
The patient advocate at my vet's office recommended this to me after Sara was recovering from a bout of "eating absolutely nothing" due to extremely high T4 levels. I'd finally gotten her to the point where she would eat human food, but needed her to get back to eating her cat food! She wanted nothing to do with it though. Then I tried Appetizers, and she LOVED them. Gave those for a couple of days, then decided to try the Fancy Feast with her again. And she ate it!
Now they are a bit on the pricey side. Anywhere from $1.00 to $1.49, depending on location, sales, etc. Definitely less expensive at the pet food stores vs grocery stores, and a bigger variety. So as merely a treat, we use them pretty sporadically (like special occasions, etc).
But if I had to go through something like cats not eating again - and I seriously hope it doesn't happen for a very long time if it does happen - I would not hesitate to buy these, regardless of how much it costs.