I'm just going to borrow some first-grade snark from this brilliant article here.
So yeah, sea cats. They're basically what you'd expect: magical beasts with a moderate amount of HD (6, to be specific), the old claw/claw/bite set of attacks, and a reasonable rake ability that can only take effect when both claws hit.Oh my, as sea cat and a sea tiger...these are most definitely not related to the incredibly lame sea lion. Nope. These are totally different and definitely not revamped versions of something Timmy drew after recess one day. I wonder if little Timmy got to design any other monsters?
Ability scores are okay, with the familiar high-strength, high-constitution, average-dexterity pattern accompanying an abysmal intelligence.
Sea cats, however, greatly diminish in usefulness once one takes a closer look at them. Their swim speed is 40 feet, which is decent, but their land speed a mere 10. Furthermore, they can't actually breathe underwater; merely hold their breath for a dozen minutes or so. This means that a sea cat can only properly function in aquatic environments where it still can surface a few times each hour. That means no underwater caverns, no plane of water, and absolutely no solid ground, which is obviously a giant limiter on in what situations sea cats are desirable characters.
To be honest, I think -0 LA is okay here. Limited range of adventuring locations aside, sea cats aren't that competitive when compared to other, similarly-leveled magical beasts. Owlbears, for example, have strictly better stats and one less HD, and manticores have flight, as well as superior ability scores.