Even in a panel or multiple round interview, it usually only takes one no to end the process for the candidate. So I don’t see how this is any worse.

For one, this one only requires the candidate to provide an hour of their time, which for me is the main reason I personally avoid multi-round interviews.

Agreed, it can also be uncomfortable for persons not of the same gender as the interviewer, so I always take a second person and try to ensure we always have a mix of men and women scheduled as that other person depending on who we’re interviewing to minimise the single point of me/another manager having a bad day.

That'd be a problem if there'd be a shortage of interesting jobs.

And, speaking as somebody who's seen a 4-digit number of interview packets: The multi-interviewer format is far from flawless, too. The capability of groups of humans to collectively fuck up without ever talking to each other is quite impressive.

If you absolutely want to invest more time, at least build a multi-hour interview that has people do their job, in a team environment. Because that's what ultimately will happen.

Don't do multiple rounds of CS trivia.

Depends.

For a small company the interviewer might well be the beneficiary of your work and in the end he needs you more than you need him. So a good one won't let his bad day ruin a nice candidate.

Also, depends on culture. There are countries where 1:1 interviews with a different gender candidate are okay.