I have seen many successful ecv's and some not so successful, I also think it depends on the skill of the doctor to how uncomfortable it can be, you are give a relaxant when it is done, and yes some babys do turn back to breech but some women also go on to have vaginal deliveries, I think it depends on yourself, like Alan said 33 weeks is still really early and the baby is still small enough to turn on its own, I wouldnt be too concerned until you get to 36-37 weeks then they will discuss your options with you. Then you will be able to make a decision based on the information they give you
Good Luck