I took these with my first pregnancy. My labor while fast for a first labor was terrible! (9 hours) I had severe need to push at only 7 centimeters, so bad that my body would physically drop/push down. By the time I made it to 10cm I was crying from the pushing sensation, it was like my whole body would contract. It made the labor sooo painful. At the time I didn't know any different. Oh also my placenta tore, which I have no idea of the cause but I suppose it could have been the herbs too.
My second labor without these was 31/2 hours and I had absolutely none of the involuntary pushing like with my first. Looking back I really think it was the herbs that did it. I personally wouldn't recommend them, but of course I can't say 100% it was the herbs.
I would do what your doing and ask stories, maybe mine was a fluke, but you want to be safe too.