This plastic baby bottle was unique among those reviewed. Made for formula users, this bottle can be filled in advance and mixed at feeding time. The Mixie stores the formula in a compartment at the bottom of the bottle. After you’ve filled the top portion of the bottle with water, a push of a button releases the formula. Simply shake to mix and milk is ready to go. This can simplify middle of the night feedings and is also an advantage when your baby is hungry and impatient. Available in 4- and 8-ounce sizes.