The parent post said that "all new team members" were subject to this. It's fine if you're willing to bring on candidates you aren't sure about on a temporary basis, but you're just going to send a lot of good candidates elsewhere if your blanket policy is "you will be terminated after a month by default". In particular, as other commenters have pointed out, you will be filtering out lots of good candidates who currently have stable jobs, but might be interested in your organization if not for the (justified or not) perceived risk of being fired for no reason.