It's not like a super instant thing or you can spawn an infinite amount of cats. It reduces the cool down to it's (more than likely) unbannable limit with no cost to spawn units.
Checked by myself.
The only effect I get is that the cooldown is less. Without mod it's something between 5 - 10 seconds till i can deploy another unit, with mod its like 3 seconds.
But they still cost money.