I had one with my last baby. I came in for my 38 week checkup and was already really dilated without contractions. The midwife offered to do a sweep and I accepted. Honestly, it was uncomfortable, but not overly so. Kind of like getting a cervical swab in terms of discomfort.
At any rate, it worked for me! I started having contractions a few minutes after the sweep, the hospital booked me in L&D and my son was born 4 hours later. The sweep gets my seal of approval.