My son loved these bottles. Once he started he wouldn't switch to anything else and they were easy to clean.
But the vent seal at the bottom was HORRIBLE quality. Constantly leaking and had to replace pricey valves often.

My son hated these bottles. I think it was the weird nipple shape they had but he would refuse to drink out of them. They leaked all the time too, so frustrating when breast milk takes forever to pump and formula isn't exactly cheap. Won't buy this product again.