You need both!
Okay, I'm a bit biased, so of course I want you to get Mystical Cats. But here's why you need both! As others have said, Cat's Eye is very real-world, with the cats in a human environment, sometimes interacting with people. It's cats as we see them, and it's a beautiful deck, made by someone who knows and loves cats.
When I set out to make a new cat tarot, I steered in a different direction ... sort of. The Mystical Cats Tarot shows you the cat's inner world, a world as imagined by cats. It's their own world, and there are no people in the deck, just cats (and a few other creatures). The book is in first "purrson" -- narrated by the cat. The cats are in four clans (Earth, Sea, Sky, Fire), each with their own culture and temperament, and the majors are the Cat Mysteries, the essence of what it means to be feline.
The settings for the cards are a magical place that Mickie Mueller (the artist) and I called the Cat Planet as we were working on it. BUT ... for all the mystical and magical in this deck, all of the cats are real cats, doing only things that real cats can actually do. (With one exception -- the levitating Floating Cat, and for all we know cats levitate all the time when we aren't looking.) That was really important to me and to Mickie. Both of us have cats and understand and love them, which I hope comes through -- our own cats (past and present) and friends' cats served as models for some of the cards.
So! You need both decks -- one for the outer life of the everyday cat, and one for the mystical world of the cat's imagination!
(And yes, the box is awful, though pretty. Go to Etsy and look for Mystical Cats Tarot. Mickie offers gorgeous bags with images from the cards, alone or as a set with the deck.)