It is a cool visit for sure if you ever get the chance to do it. I would say to make an appointment ahead of time, not just for the "popping in" aspect, but just to try to time things on a production run day or something. When I was there, there wasn't any production stuff happening on the line. I did get to meet a number of people, and they were working R&D stuff (like I got to see the Axiom Air way before it was ever released and while in a beta form. I even got to do some blind A/B listening and pick which sound I liked better. Found out afterwards that I was listening to one of their prototype speaker configurations for what would eventually become the production Axiom Air vs. a pair of regular M3 speakers.
So yeah, I would plan ahead and call them to find out when a visit would make sense so that you could see things in action. I still got the full tour, but why not see the lines running...
