Hi,
I had one to one in my last pregnancy (can't get it this pregnancy due to location but would in a heart beat).
They differ from usual nhs community midwives in that they are case loading midwives I.e. You see the same 1/2 (you will have a 2nd midwife in case other is sick etc) all the way through pregnancy and up to 6 weeks postnatally. They see you at home. You are still entitled to access everything that you would if in usual NHS care. You have their mobile number if you need anything at all and can ring/text them whenever.
I disagree with pp saying that you shouldn't use them if you don't want a home birth. Their whole philosophy surrounds empowering women, informed choice and individualised care - they are there to support wherever you want to birth. If you choose home birth then yes, you will know the midwife who will be there when your baby is born, if you choose to give birth in hospital, they can actually come to your house when your in early labour to support/assess you before you go into hospital.
I had an elective section. I saw the same midwife at every appointment who knew me, my history, what issues I was facing personally etc. (This pregnancy I have seen 6 different midwives who all give different information). I saw the one to one midwife regularly (this pregnancy, I have gone up to 6 weeks between appointments; I would see my one to one every couple of weeks after 24 weeks). After my section, my one to one midwife visited me in hospital and supported with breastfeeding (I had some difficulties even though I had bf my first) and then visited me every day for about 5 days then at regular intervals after that (nhs usually discharge you at 10-14 days and often expect you to go to a clinic to see them and again, you are likely to see a different MW each time).
For me, the service was out of this world- it was like and independent midwifery service for free. I have really noticed the difference with this pregnancy and feel like I was thoroughly spoiled last time! For me, the continuity is worth its weight in gold