If you're considering purchasing the Formula to get the beasts (and not just for the story), here are the highlights:

Firstly, none of the 5 beasts are particularly good in main stats. Don’t use the card-based selling options either, just sell them normally.

The Ocelot’s card helps immensely when you’re grinding SotC to 10, and saves a typewriter when setting up your newspaper for the first time. After that, the value is minimal.

The Dream-Hound’s two cards are amazing (4E of honey and a full Wounds heal), and saves you a Bengal Tigress when upgrading your Parabolan defenses (same as the Dream-Dwelling Carnivorous Aurochs from Whitsun). Get this one first.

The Stallion’s required to move the story along, its card is good if you like to gamble, and you can hide the card much later in the game.

The Toadbeast... is part of the Owl.

And finally, the Owl is tied with the Ubergoat for BDR at +4, exactly 1 more than all of the top-tier Whitsun beasts. It can also assist with the SotC grind, if you're not already done by the time you get rid of the Ocelot.