CRBA interview at U.S. embassy in London

[chesterming]

I am wondering how the interview for a CRBA goes. Is it just to check all your documents are in order, or is demonstrating to the consular officer that you have the required physical presence by showing them the relevant proof? Given that they ask you to bring an envelope with postage paid for, does that mean they make a decision after the appointment, or do they let you know right then and there if they don’t think your proof is enough to transmit citizenship? I’m also curious to know how strict officers are, and if they may deem certain pieces of proof as insufficient or not, or does it depend on the officer themselves? Any information would be greatly appreciated.