With my middle child, I had it done twice and it didn't work.
With my last child, I was 38 weeks, 2 days and started having contractions on the way to my appointment. She checked me and I was at a 3 so she stripped my membranes then I went and walked around for about 3 hours. I went into labor later that night and had her the next day.
Oh ouch! midwife did one on me when I was in labour, without even asking or telling me what she was gona do! I was in labour about 28 hours at that stage tho + still only 1cm dilated (grrrr!!!). I dilated to 3cm straight away then but had other complications so ended up having an emergency c section. I know girls it worked for though they dilated pretty fast + waters broke on their own. Not mine, they had to be broken by another midwife who also didnt tell me what she was gona do!