"unlimited" days off are nonsense. Can I take off 365 days a year? If the answer is no it's not unlimited. There's a limit, you're just not specifying it.
Sure, but my point is if you can be fired for taking too many days off, it's not unlimited. It's limited by the amount of work you're expected to reasonably do, and that's decided by your boss and colleagues. Except now instead of having a hard number where you know you are safe, it's completely subjective how many days off you can take.