I received this used from a friend (who has a 3 year old) and have been using it for 5 months. It works great! The reference card tells how much water to put in, and the bottle is warmed perfectly! (We use Dr. Brown's glass bottles, and have had no problem).
Minus one star because - You MUST clean it once a month with the vinegar solution or else the heating element gets gross. (1 oz vinegar to 4 oz water, let sit.) Of course that may be because ours is several years old.
True, the beeping is loud, but since we have it in the kitchen I can throw a bottle in, then run over to the bedroom and change the baby, and still hear the beep, so for me, it's perfect. I'm going to buy another one for visits to grandma's house, as well.