That's a legit question and I don't know the answer. However how is it different from hiring someone and letting him go after a month if you think he's not a good fit? The mention of a month of bootcamp or "orientation" is mainly to set expectations.
You should always hire the best candidate which you think will work out but that month allow you to set the right phase, this is a month where you both give the best to make that relationship work - orientation, pairing, documentation, short meetings to discuss potential roadblocks or issues.
All startups usually do this - I just consider it's a good practice to say it out loud that there's a period where we both find out if we want to keep working together.
You should always hire the best candidate which you think will work out but that month allow you to set the right phase, this is a month where you both give the best to make that relationship work - orientation, pairing, documentation, short meetings to discuss potential roadblocks or issues.
All startups usually do this - I just consider it's a good practice to say it out loud that there's a period where we both find out if we want to keep working together.