Pros: Baby had less gas, breast milk didn't stick to it as much, made of less chemicals
Cons: Too many parts at times, the measurements rubbed off quickly
I used these for my daughter almost right away because I was a full-time pumper. I was using other bottles before and found that she got really gassy.
They worked really well (as well as the glass ones) for allowing the breastmilk to not stick to the walls and are a great alternative for times that you are going out and do not want to risk breaking the glass bottles.
Even though there were a lot of parts, you can get away with just putting them in a bowl when you are done and letting them soak in boiling water for a bit.
I found that they almost instantly got rid of my daughters gas, caused by other bottles and she never had gas.