With my first it worked perfectly fine but I gave birth this morning and got it around this time last night I still felt contractions on one side they had to give me a higher dose then I was okay lol so it depends really.
When I say I could feel everything I mean that's where my contractions went to for whatever reason. I had never heard of it before so it was really weird to me and I remember constantly saying "my buttcheek hurts" but it's the only way I knew I was having contractions to be able to push.
Yes, mine didn't work at all at one point, they had me roll on my side and it slowly started working but I could still feel everything in my left leg/buttcheek. It was completely awful and so painful but I guess at least it worked on one side so I wasn't completely miserable.