I loved using the Playtex Drop-In bottles and liners. Not only did I see improvement with my sons gas but he was picky with size of nipple and only took to ones closest to mommy's boob. I chose these one's mostly for convenience but I was also happy with them. I exclusively pumped so having to wash and sanitize less saved me a lot of time wasted away from my baby and other things. They are an extra cost for liners but worth it for the convenience. Two minor negatives: 1) over time the lid doesn't snap on tight so once you see that starting to happen I would recommend putting saran wrap or something over top to give it that extra grip to snap on and stay tight, especially if traveling with them). Nice and light also and easy for baby to hold due to the slight curve in bottle. 2nd negative: The measurements are slightly off 1/2-1oz. Because you poor your breastmilk or formula into the bottle liner, the measurements are off because the liner doesn't fully expand to the width of the bottle. This wasn't a big issue for me as I stored in glass and premeasured before pouring for feeding. I found that when you pour 5oz of liquid into your bottle with the drop-in liner it will read more because the measurements are made based on the actual bottle not the filling of the liner - if that makes sense. A bit of an annoyance but wasn't a deal breaker for me. Lid also snaps on bottom of bottle when feeding so that was handy and prevents misplacing.