It's a slightly more explicit version of a probationary/trial period, which is very common outside the US. (You don't need them in the US, because you can be fired at any time for any reason anyway.)
This. I've had to fire someone in their probation period, and their expectation (that they had finally landed a great job and could relax) clearly didn't match our expectation (we had a new employee on probation, let's see if they work out).
It would help people more if there was a clearer expression of "this is a trial. You might not pass it".
It would help people more if there was a clearer expression of "this is a trial. You might not pass it".