Hungry baby formula (repeated)

Ok, so I have now been advised by many people to switch Ruby onto hungry baby formula. Everyone seems to think that this is just what she needs to feel fuller to sleep longer. I did try a bottle and low and behold she slept for 45 mins after. I then called and Aptamil and asked their advice. The lady I spoke to told me not to give it to her again, and that it was only for babies who are drinking 8-9oz per bottle and crying for food within a short space of time. I am lucky if Ruby takes 6oz's per bottle. She is loving food and I have now introduced a cube after her afternoon bottle of either carrot or apple. She doesnt have a lot but would have more if I let her (she is nearly 20wks).
Anyway what I am trying to ask is how many people are using hungry baby formula? If you are using it is it because your lo's are downing 8-9oz's per bottle and still hungry or is it for the same reasons as I am being advised? Thanks xxxx