Definitely a trap. My husband just started a job at a place with unlimited PTO; we knew this going in, and were sad. When anyone wants time off, they have to send an email to the entire group telling them, and anyone can object. So much worse than just getting your manager’s approval for days off that you have already earned!
At my current workplace, I started getting 25 days off per year when I hit 10 years’ service. Now THAT’s good stuff.