I began using the 9 oz AVENT bottles about three weeks after my son was born. After breastfeeding for three weeks to a baby that always seemed hungry, I bought a Medela breast pump and switched him to the AVENT bottles and we both have been happy campers ever since. Occasionally I do have a problem with leaks, but that mostly seems to be when I do not insert the nipple under water. On average, I keep 9-10 bottles of breastmilk in the refrigerator ready to go and immediately wash or rinse the bottle/nipples after each feeding and have not had any problems with cloudy bottles or nipples. I did not purchase any of the extra supplies such as warmers, storage containers from Avent. To warm a bottle, I use warm water which will warm the milk in about 10 minutes. I would definitely recommend these bottles to any new mother.