I wasn't trying to sound rude about the drop-in question?

Question

I was seriously wondering what they are for, what's the difference between using that then just mixing warm water and formula?

Answer 1

you are confusing type of bottle and type of formula (powder, premixed). A drop in is a type of bottle....

Answer 2

Drop ins are great because you don't have to wash and sterilize the bottle each time. But if you do use please recyle the liner insead of throwing in the trash.  

Answer 3

They are for the baby to drink formula out of. It works just like a bottle, except there is no bottle to clean, as you simply throw the used liner away when your baby is finished with it. The formula only comes into contact with the nipple and the liner, so the bottles and rings can be re-used without needing to be sterilized. I still run mine through the dishwasher every couple of days when I sterilize the nipples.

Many moms like it because it is more convenient to just throw the liner away rather than wash the bottle. All you have to do is use a new nipple and a new liner and it's easy as pie.

Answer 4

Drop-in are for gassy/colic babies, my son used playtex drop-in they are amazing! cause regular bottles make him very gassy while air are in the bottles. If you want drop-in to make a warm bottle, used hot water to make drop-in bottles or used bottle warmer.