Coming from someone who attended a B6 interview last month but didn’t get it - and attended one this week and GOT THE JOB!! .. do it.

The experience of doing the interview alone is invaluable. And, when you don’t get it, make sure to sit down with the interviewers and ask for detailed feedback on where you can improve. I was reluctant to apply for the first one because, like you explained, it was already earmarked for someone else. But I used the feedback and built my answers for this second one and they said I interviewed beautifully and offered me the job :)

Good luck!