I thought I'd make a short post about them to a) remind myself in the future, and b) help someone that had the same problem I had. Hey, if this benefits even one person, it's worth it.
Problem: At a week old, Jack started flattening the nipple on the bottle. I wasn't sure why. I thought maybe the flow was too slow, but that's not possible - the next flow is meant for a 3-6 month old. It took him 45 minutes or more to guzzle a mere ounce and a half. He was creating a vacuum with his mouth and the nipple. He was extremely fussy and gassy (to the point where the doctor thought he probably had colic) and we were frustrated.
Solution: After an extensive amount of research, we almost splurged and bought the expensive Dr. Brown's bottles, meant for colicky babies. But I'll admit I'm a cheapskate and a bit lazy and wasn't too thrilled about washing five pieces of a bottle after every single feeding, so I held off a bit and kept researching. Then I came across one review on Amazon that mentioned the ring of the bottle. They said to make sure you don't tighten it too tight or the bottle will not ventilate correctly, causing your baby to inhale a lot of air. A lightbulb went on in my head. I had been tightening the ring pretty tightly so the bottle wouldn't leak (makes sense, right?). But that was my problem. Once I started screwing the nipple and ring on looser, allowing it to ventilate, our problem was solved! (Make sure when your baby drinks that you see little bubbles coming back into the bottle.) I'm so glad I figured that out and thus am able to keep these glass bottles which I so dearly love.
And Jack is a TON happier - his temperament has improved greatly! He isn't colicky at all!