I did it when I was overdue with dd and I didn't go into labour but I was 4cm dilated when I went in to be induced, so it did make a difference. It took 8 hours for the induction to work so she really wasn't keen on coming out!
I did it the day after ds2 was due and went into labour immediately! I'd seen the mw in the afternoon and he wasn't engaged or anything so I couldn't even have a sleep - I did the nipple stim from 10-11pm, went to bed, had a contraction just after I got into bed, another 6 mins later, another 4 mins later, thenm they went to 2 mins apart and he was born at 1am. So I'd say it works .
I used a breast pump (felt too weird to do it myself!) and did 15mins on one side, 15 mins on the other the swapped over so I'd done an hour. It's boring and the colostrum goes everywhere. Apparently you shouldn't do both sides at a time because it can distress the baby.
It does induce quite string twinges after you've been going for a bit. I had to stop for a bit as it got too painful. They do ease when you stop, unless it puts you into labour!
It's worth trying as it gives you something to do but like all DIY induction things, it'll only work if you're ready to go into labour anyway.