I had this done last week so thought I would chime in :)
The procedure is called External Cephalic Version (ECV for short) and people have different opinions on it including medical professionals. Some hospitals won't do it, some will. There are people who have found it very painful and others who have had virtually no pain. My mum had it done at 34 weeks with me successfully and it was very easy but I was quite small.
For a small percentage (around 1 in 1000 women) the procedure will cause them to go into labour and they need an emergency c-section. You are well monitored whilst the procedure is happening to make sure baby isn't in distress and if he is then it will be a section.
When I went to the hospital I was given a presentation scan by the midwives to see what position baby was in (extended breech for us). Then I went to labour ward which is where they do the procedure. I was hooked up to a monitor to do a trace of baby's heartbeat for 20mins. Bloods taken, blood pressure done as well. I was given an injection of turbutaline (unsure of spelling) to relax my uterus/womb.
Doctors then came in and explained what would happen. Two doctors put a lot of ultrasound gel on my tummy, checked where baby was with a scanner and then began the procedure. They were basically trying to pick baby up and turn him. It wasn't comfortable but was only for a few minutes at a time, they tried 3 times. I have quite a high pain threshold and just kind of get on with things so I zoned out staring at a mark on the ceiling, and breathing through it. It does feel quite invasive but nothing I couldn't handle (I know this will vary from person to person). I was 37 weeks.
The procedure didn't work. I felt very tender afterwards and for the next few days. I have been told it works in 50% of cases. Our baby is very stubborn! After it, I was scanned again to check baby and hooked up to a monitor again for half an hour to make sure baby wasn't in distress.
I was called the next day to be given the date of my c section.
Overall, I was glad I gave it a go. If you search for ECV on Mumsnet you will see different opinions. 10% of turned babies turn breech again after the procedure. Well, that's what I was told. Statistics probably vary.
You have the option to turn down the procedure if you aren't happy about having it. You can also have it done and stop halfway through if it's too uncomfortable.
There is a tiny risk of something going very wrong and losing your baby. It has happened to some women. It's whether you feel the risk is small enough to give the procedure a go.