Its not better job security. Your best job security is to show up and do your job. I have seen union turds get fired too. It just depends on how much your managers are willing to put up with. Plus, I have seen people join just to get their job back if it ever really becomes an issue
Oh
! and the Christmas party the drinks are not free. Not even like 1 or 2 on the house. They are not cheap. The Christmas party food might be like 20$ value. Throw in the entertainment and swag, I'll bump it up to 50$ value. You are going to pay over 300$ just in your first year, and I know people paying 25$ a week in union dues.
I also forgot. The safety comity is union run, in theory. If you have a safety comity, you can ask about joining it if no one in your area is on it. You get paid for it, and it would probably pay your union dues. But you still have to go, and there is paper work. Most people just make stuff up to fill it out, instead of making real observations. Either way its still your time and money. Some places will exclude people that are not in the union for the comity.
Perhaps not the end all, be all but you have to wonder... Would your pension be as good without it?
They could still pull a hostess. I don't "have" a pension till its cash in my hand.