Wouldn't this self select for the unemployed? Unless they took a week off and then gave notice after the "contract" period.
To be cynical perhaps an unemployed person has less negotiating power, so you can get higher quality diamonds in the rough cheaper.
The classic fear is the person is unemployed for a flaw in that person, but perhaps this trial alleviates that somewhat?
Whether that is good or not, I leave it up to you.