Dunno how effective they are as I never had one myself but from watching all those baby birthing shows on tele, I can say that every one of the women on there who are in agonising pain all of a sudden can handle the labour & seem much happier once the epidural had been done.
My sister had one & asked them to keep it in for a few more days as she was loving it so much & other friends who have had it say that you still feel the pain & pressure but it is totally bearable where as without one they felt like they are going to die of pain!!!
I'm having one but have been encorouged not to have it too early (which is fine) but as soon as I feel I need it I am going to get it.
Don't forget, your mw is there to advise but it isn't her descision in the end. IT'S YOURS.