I'd like to say 'it can't hurt' but my first sweep did!
I had lots with my daughter (she was 16 days late, I had 10!) and this time I am going to refuse them as they clearly did sod all for me and I think caused some swelling with so many.
But I know lots of people who feel their labour has been triggered by it and swear by them, and at least it's not chemical. I think they only work if you're pretty much ready to go anyway.
Not for me but it's a personal decision.