These are so great! I bought a bunch of glass bottles, including life factory, thinking to use them for pumping. My daughter won't take a bottle but she sure loves her sippy. So I bought these, and they work several of the bottles I have so I didn't waste the money. These don't spill at all either.
I was excited to buy these so I could turn my daughter's bottles into sippy cups, however they don't seem to work very well? I tried to drink out of one myself and it was really hard to get the liquid out. Maybe they get better over time... I had to remove the silicone piece inside the lid in order for her to get any liquid out, but the downside is that it leaks all over the place if turned upside down.