I'm more worried about in person because they don't know my lifestyle choice and I would hate to get to talking to someone and then they run.
It might be unpleasant, but if poly isn't for them, the best thing would be for them to bail early on, so neither of you are wasting your time and getting attached when it was never going to work out at all. Online is easy, nothing invested and if they read your profile, it's right there at the top. In person, if you feel a connection, you can still tell them electronically if it's difficult to talk or awkward to bring up in person. My husband PunkRock and I met, and then he friended me on Facebook. We started texting through Messenger that night, and I asked him if he knew my situation, and then I let him know about my husband DarkKnight. He was surprised and said well he wasn't interested in dating right then, because he had a lot going on, but he was mainly thinking we could be friends. So we were text buddies for like a month and I went out and dated LOTS of guys. Then, he decided he would give poly a try, we went on a date, and it was obvious right away that this was going to work.
That said, I have met plenty of other guys in person who were initially interested, but when I bring up poly, they back away. That's okay. As hot, or as interesting, as they might be, it just means we aren't compatible. We both move on as dating partners, but in some cases I have made some good friends.
Good luck on your date!