S.T.
I have a 10 mo. old that was exclusively breast-fed until 9 mo. when my milk supply started decreasing. He now gets one bottle of formula per day in addition. I was working, though, from 2mo to 4mo, and had to pump. He did fine with the playtex drop-in system, but it is important to use the latex, slow-flow nipples (the brown ones). they are the most like the breast. I have used the breast-flow bottle with him on occasion, but he really does much better with the playtex. I hope this helps! Also, it makes a difference if they are drinking breastmilk or formula from the bottle when trying to switch from breast to bottle and back. Good luck!