> Candidate would be compensated, obviously. That's why it's expensive

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.

And so that self-selects for people who already are unemployed then, right? Most developers I know (including myself) look for a new job while still having a job, as to not create a financial hole in-between. I'd be curious if that doesn't then end up with lower quality candidates who ended up unemployed to begin with?

I'd argue the bigger expense is on the team having to onboard what could potentially be a revolving door of temporary hires. Getting a new engineer to the point where they understand how things work and the specific weirdness of the company and its patterns is a pretty big effort at anywhere I've worked.

> can't start contributing after a week.

Because you have zero context of what the org is working on.