I thought I "had to have" the bottles that had the slider on the side to slide the bag up and air out..well..those sliders don't slide the bag evenly, they actually get stuck and are totally useless. More importantly - the tops of the bottles shread and break off leaving little pieces of sharp hard plastic on the top of the bottle. It almost looks and feels like glass - very dangerous! (happened on 6 out of 8 bottles that I have) However, I also use other playtex drop-in bottles (the old fashion looking ones) the plasctic is NOT like glass and they are wonderful! Go with what is safe and what works rather than appearance, I didn't at first and regret it :)