This is full of TMI:
How a sweep feels depends on quite a few things - like the position of your cervix. I found it incredibly uncomfortable because my cervix sits in a slightly hard to find place (the nurse always has trouble during smears), and it was very short and closed. I actually cried
but didn't in labour. It's a completely different kind of pain.
I guess it would be useful for practising your breathing because you really need to relax, and having someone's hand inside your vagina, and their finger sweeping around your cervix is much worse than a cervical smear.
I'll have one again if I go past the due date, or have another two-week latent labour, but only one. Don't think I could do it twice in a short time. The nearly two-year gap since I last had one is long enough to fool myself that it's not as bad as I remember.
BTW: the MW was fairly confident she wouldn't have to do it again because she got a fair amount of my mucus plug out when she did it. So if you have one and see the plug then feel happy!