These bottles are wonderful for breastfed babies and I'm willing to bet that they would also work wonderfully for formula fed babies. I heard about them through a Mom's group on Facebook and chanced it by only registering for this brand. When my one week old had a tongue and lip tie that caused extreme pain while nursing, we tried using these bottles to give Mom a break. Luckily he took to them immediately and now at 4 weeks old still going strong! Baby also goes easily between bottle and breast, something we worried would cause an issue. We use paced bottle feeding (technique for exclusive breastfed babies to help mimic the breast) and these bottles made it super easy for Dad and Grandmas to use this technique. Also love that baby does not seem any more gassy after using these bottles, he seems just as content as after breastfeeding.
We did try a different brand that was gifted to us and do not like them as much. I especially like that the flow is not too strong for a breastfed baby and that they are made of silicone which holds up amazingly in the dishwasher. Highly recommend these!!