Horribly unprofessional.
Applied and got a request for an interview. Scheduled the interview using their scheduling tool. On the morning of the interview I got a request to reschedule. This happened five more times, an hour or two before the scheduled meeting time I'd get another request to reschedule the meeting. I'd set aside part of my day for the interview and then it would be rescheduled.
They also sent me a list of questions, which I answered, and then they sent me the same questions again. It was clear they weren't serious about me as a candidate.
The entire experience was unprofessional. No legitimate company would treat candidates this way. I finally I sent a note telling them I was not interested in working with such an unprofessional company.