I had my K-1 interview today and it was approved. This was literally the part of this process that intimidated me the most, but it was by far the easiest.
Line up early!! By 7:15am the line is already quite long. Stay at the Courtyard Marriott as it's literally a block away and Montreal traffic is horrid.
Make sure to have a copy of your passports biometric page. I didn't read that I needed that anywhere, but being the neurotic organized person I am I wanted to have everything I needed plus a whole lot more of things I might need (and duplicates, just incase.)
Also, bring the proof of paying for the DS-160. I had that (luckily) but also didn't realize I'd need that.
Aside from waiting outside, the whole thing was wrapped up in about 30 minutes. The interviewer was a young guy and I think I lucked out with him bc he was really personable and just made it seem like a nice conversation rather than a government grilling :-)