You don't need him to become efficient. Also I don't think it is always necessary to have such long onboarding. I'll never understand why a new hire (at least in senior position) can't start contributing after a week.
Ok... take me through it. I apply to your company and after a short call you offer me to spend 4 weeks working at your place instead of an interview.
I go back to my employer, give them resignation letter, work the rest of my notice period (2 months - 3 months), working on all handovers, saying goodbyes.
Unless the idea is to compensate me for the risk (I guess at least 6 months salary, probably more), then I do not see how you'd get anyone who is just a poor candidate to sign up for this.
> You don't need him to become efficient
So what will you see? Efficiency, being independent and being a good team player are the main things that are difficult to test during a regular interview.
You can say that about all forms of hiring process. If you're unemployed, you obviously have more time: to spend more time on the take-home assignments (which I hate, see another thread [1]), to add more stuff to your GitHub profile, to go to more interviews, etc.
Yes, but there's a significant difference between spending a few hours on a take-home assignment and dropping your current employment to spend 4 weeks potentially in another city working full time.
Because you have zero context of what the org is working on.