we are FF from birth and used avent from day dot with DD....

have had no issues with them at all, the only thing i find is if i do the lid up to tight they leak, but i obviously know about that now so dont do it

we also have the avent electronic sterilizer and love it, so handy! it keeps bottles sterilized for 24hrs, so i can put them on at night and then know they are fine till the morning.